Strategic Materials: Technologies To Reduce U.S. Import ...

CHAPTER 7

Substitution Alternatives forStrategic Materials

ContentsPage

Roles of Substitution in Materials Use. .. ...263Substitution as an Emergency Response to

a Supply Problem. . ..................264Substitution as a Continuing Strategy for

Reducing Import Vulnerability. . . . . . . ..264Factors Affecting the Viability of

Substitution . . . . ...............,.....265Technical Factors. . . . . . . . . . . . . . . . . . , . . .265Economic Factors . . . . . . . . . ...,.........265Institutional Factors. . ..................265Designer and End-User Acceptance .. ....266

Summary of Substitution Prospects . .......266Prospects for Direct Substitution in Key

Applicat ions . . . . . . . . . . . . . . , , . . . , . . . .268Chromium Substitution in Stainless Steel .268Chromium Substitution in Alloy Steels.. ..276Reducing Cobalt and Chromium Used in

Superalloys for High-TemperatureApplicat ions . . . . . . . . . . . . . . . , . . . . . . . ,277

Advanced Materials . . . . . . . . . . . . . . . . . . . , .285C e r a m i c s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 8 6C o m p o s i t e s . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 0 1Long-Range Order Intermetallic Materials .313Rapid Solidification . ...................314

Institutional Factors in Substitution . . . . ....318Information Availability and Substitutes ..318Qualification and Certification of Alloy

Subst i tutes . . . , . . . . . . . . . . . . . . . . . . . . .319Institutional Barriers and Advanced

Materials . . . . . . . . . . . . . . . . . . . . . . .., ..323

List of TablesTable No, Page

7-1.

7-2.

7-3.7-4.

7-5.

7-6.

7-7.

Examples of Substitution Relevant toStrategic Materials . . . . . . . . . . . . . . . . 263Primary Motivations for SubstitutionR&D . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266High-Volume Stainless Steels . . . . . . . 269Development Status of PotentialSubstitutes That Could ReduceChromium Requirements in StainlessSteel . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271Ladle Analysis Ranges for theChrome-Free ReplacementCompositions for Standard 4118 and8620 Steeds . . . . . . . . . . . . . . . . . . . . . . . 277Typical Structural Alloys Used forHot-Section Components. . . . . . . . . . . 280Nickel-Base Superalloys Selected forCobalt Substitution Research byNASA . . . . . . . . . . . . . . . . . . . . . . . . . . . 283

Table No. Page7-8. Use of Structural Materials Under -

7-9(

7-1o,

7-11,

7-12.

7-13,

7-14,

7-15,

7-16.

7-17.

7-18.

7-19.

Figure7-1.

7-2

7-3,7-4(

7-5.7-6,

7-7,

7-8.

Development to Reduce Cobalt andChromium Usage in Hot-SectionParts . . . . . . . . . . . . . . . . . . . . . . . . . . . .Current and Prospective Uses forAdvanced Ceramics . . . . . . . . . . . . . . .Some Advanced Ceramics MaterialFamilies . . . . . . . . . . . . . . . . . . . . . . . . .Potential of Advanced Ceramics toSubstitute for First-Tier StrategicMaterials . . . . . . . . . . . . . . . . . . . . . . . .Advanced Composite MaterialsOptions . . . . . . . . . . . . . . . . . . . . . . . . .Price Range of Selected CompositeRaw Materials . . . . . . . . . . . . . . . . . . . .Current Aircraft Applications forAdvanced Composite Materials . . . . .Potential Commercial Applications ofMetal Matrix Composites . . . . . . . . . .Potential Automotive Applicationsfor Composites of Kevlar 49 Aramid.Current Status obtesting ofModified 8Cr-1Mo Steel Tubes inU.S. and Foreign Steam PowerplantsStatus of Specifications for Modified9Cr-1Mo Alloy . . . . . . . . . . . . . . . . . . .Structural Ceramic TechnologyFederal Government Funded R&D...

List of FiguresNo.Temperature Capability ofSuperalloy . . . . . . . . . . . . . . . . . . . . . .Temperature Capabilities of TurbineBlade Materials . . . . . . . . . . . . . . . . . . .Graphite Fiber Cost . . . . . . . . . . . . . . .Fiberglass Composite Applications . .Carbon/Carbon Composite Needs . . .Development of Modified 9Cr-1MoSteel for Fossil Fuel and NuclearPower Applications . . . . . . . . . . . . . . .Technology Transfer Ladder for ODSMA 6000. .. . . . . . . . . . . . .Technology Transfer Ladder forCOSAM Strategic MaterialSubstitution . . . . . . . . . . . . . . . . . . . . . .

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CHAPTER 7

Substitution Alternatives for Strategic Materials

Roles of Substitution in Materials Use

Designers choose materials that they thinkoffer the most attractive combination of serv-ice performance and reliability, ease in proc-essing and manufacturing, cost, and availabil-ity. However, these factors constantly changeas new materials with better properties are de-veloped, better information about existing ma-terials becomes available, new processing tech-niques are developed, and relative costs andavailability of materials fluctuate. Substitution,the process of revising the match between ma-terials and applications, is the material users’technical response to this shifting environ-ment. In some cases, substitution involves find-ing or developing the best material for the ap-plication (replacement); in others, it involvesdesigning or redesigning the application tomake the best use of available materials.

Substitutions can be very costly and there-fore are undertaken only when there is a highdegree of certainty that the benefits will be sub-stantial. To be adopted, a substitute materialor design must demonstrate both technical andeconomic feasibility and must overcome a va-riety of institutional hurdles. More important,it must gain the acceptance of the designersand end users who will ultimately use it.

Even though substitution includes both re-placement and redesign, current strategicmaterials-motivated substitution research is,for the most part, oriented toward developmentof alternative materials that have less strategicmaterial content.l At present, considerable re-

I Th(] ugh product design and redesign can be used to reducestrategic materials requ i rernents, this strategy is less amenabloto a centralized research effort because of the vast number ofproducts [and the case-by-case nature of this technique). Newmanufacturing process designs can also rfxluce strategicm a ter ia ]s needs i n some applications, However, these sa \’i ngsare rare] y the prima r}’ m oti \’a t ion for process d e~. elopm en t orimplcrnf?ntation dnd are not realized if greater cost or perform-an(:e advantages lie with other processes. As a national strat -

search—most of it government sponsored—isfocused on development of replacement ma-terials that could reduce strategic material re-quirements in several critical applications.These include, among others, several lowerchromium alternatives for existing stainlesssteels now used in powerplants, chemical proc-essing facilities, and other applications wherecorrosion resistance in a range of environ-ments is needed; low- or no-chromium alloysteels for bearings, gears, shafts and other high-stress, long-service life applications; and low-or no-cobalt superalloy for gas turbine appli-cations. Some examples of substitutions thathave been or could be important to strategicmaterials use are shown in table 7-1.

Table 7-1 .—Examples of Substitution Relevantto Strategic Materials

Direct material substitution:Ceramic magnets for aluminum-nickel-cobalt magnetsDolomite for magnesia-chromite refractoriesInterchangeability of platinum-group metals and gold in

electronic componentsModified 9% chromium-1% molybdenum steel for 18%

chromium-8% nickel stainless steel in reactor vessels,heat exchangers, and tubing in powerplants

Polymeric materials for decorative chrome in automobilesCobalt-free superalloy for 56% cobalt superalloy in JT-9

jet engineProcess design substitution:

AOD vessel for double-slag in stainless steel makingPrecision casting and forging for machining in parts

manufactureContinuous casting for ingot casting in steelmaking

Product design substitution:Ceramics in experimental automotive gas turbine enginesDownsizing of turbine engines made possible through the

use of lighter materials in aircraft components——S–OURCE” Off Ice of Tech~ology Assessment

—.egy to reduce U.S. dependency on imported materials, produ(:tor process design modification can on]}’ be succf?ssful i f df~signengineers can be convinced to include strategi(, materials sa\-ings as an i rnportant objective in design decisions.

263

264 ● Strategic Materials: Technologies to Reduce U.S. Import Vulnerability

Substitution as an Emergency Responseto a Supply Problem

To a certain extent, already developed, on-the-shelf substitute materials and technologiescan be relied upon in an emergency to con-serve materials that are in short supply. As dis-cussed in chapter 3, substitutes for strategicmaterials in many applications are often avail-able, though not necessarily readily recogniza-ble as such. Alternative materials could be usedin these applications with low (or at least toler-able) penalties in performance and cost. Thematerial saved through these measures wouldthen be available for use in critical applicationswhere higher or unacceptable penalties areassociated with substitution.

The existence of technically and economi-cally viable substitutes is not the only require-ment for a timely response to a supply emer-gency. For many critical applications, a newmaterial must be tested and its use in a par-ticular component must be qualified (acceptedby the consumer) and certified (shown by theproducer to meet the consumer’s require-ments). Thus, immediate response is limited tothose materials that are already in (or very closeto) commercial use, and to applications that donot have stringent materials requirements orfor which the material has been certified andqualified. The substitution response by U.S. in-dustry to prior supply problems involving stra-tegic materials is discussed in chapter 4.

The current ability of U.S. industry to re-spond to a supply problem with substitutionis not known with any degree of certainty. Al-though a large backlog of alternative materialsand technologies is generally conceded to ex-ist, information about many of these potentialsubstitutes has not been assembled in a system-atic way which would be accessible to design-ers, material users, and decisionmakers in anemergency. Development of a substitution databank or a materials information system thatwould bring available substitutes to the atten-

tion of engineers and designers is one frequent-ly proposed means for reducing U.S. vulnera-bility to an import curtailment. This conceptis discussed further in chapter 8.

Substitution as a Continuing Strategy forReducing Import Vulnerability

Besides being an emergency response, sub-stitution can also play a key role in long-termstrategies to reduce dependency on importedmaterials. During the last decade, there hasbeen much research focused on developmentof substitute materials that could reduce stra-tegic material requirements for many alloyscurrently used in key applications. Other re-search has been aimed at development andcommercialization of advanced materials (e.g.,ceramics and composites) which may displaceuse of strategic materials in some applications.

Although many technically promising substi-tutes are under development, the extent towhich they will be adopted by U.S. industryis difficult to foresee, In the absence of animmediate availability problem, industry’sadoption of new materials, designs, and man-ufacturing technologies is usually not moti-vated by concerns about strategic materialsavailability. Generally, the new technologieswill be used only if they offer some more im-mediate benefit such as reduced costs, in-creased outputs, improved product perform-ance, or potential new products.

A successful long-term strategy for reducingU.S. vulnerability to imported materialsthrough substitution depends not only on thetechnical feasibility of alternative materials buton acceptance of them as practical alternativesby industry. Acceptance comes only when thetechnical and/or economic benefits have beenclearly demonstrated, various institutional bar-riers have been surmounted, and a high degreeof designer and end-user confidence has beenestablished.

Ch. 7—Substitution Alternatives for Strategic Materials ● 265

Factors Affecting the Viability of Substitution

Technical Factors

Over time, a backlog of proven, on-the-shelfmaterials and technologies have been devel-oped that for one reason or another have notbeen adopted by industry, Research and devel-opment (R&D) efforts by public and privateagencies throughout the world are adding tothis store of potential substitutes almost daily.Only a few of these are likely to be adopted byindustry at any given time.

Technological barriers to strategic materialssubstitution can be time-consuming and for-midable, especially for applications in whichlittle or no compromise in performance isacceptable, Even when a promising substituteis developed in the laboratory, new and signif-icant technical problems may be encounteredwhen large-scale tests are undertaken to ver-ify laboratory findings, Often, a return to basicresearch is required to overcome these scale-up problems. Additional technical problemsmay be encountered when full-scale industrialproduction is begun.

Economic Factors

The technical potential of substitution to re-duce strategic materials requirements is fargreater than what is economically feasible. In-dustry will not adopt technically promisingalternative materials unless they are cost-effective compared with current materials.Often, the cost effectiveness of using the cur-rent material is not greatly affected by priceincreases in strategic raw materials. In fact, theprices of raw materials can be such a small partof the cost picture that they are relatively unim-portant in a substitution decision. For exam-ple, raw materials account for only about 1 per-cent of the cost of a jet engine, Even platinumgroup metals (PGMs), which cost between $100and $400 per troy ounce, account for less than5 percent of the cost of products manufacturedwith PGM catalysts. Therefore, all else beingequal, a change in the cost of raw materialsoften has to be dramatic to warrant the expense

of shifting to a substitute material. Adoptionof a new material may require costly newequipment or changes in operations. There arealso costs associated with change itself—fortraining workers in the use of a new materialor process, for changing the design of products,and for adjusting manufacturing practices.

Institutional Factors

An alternative material may take a decadeor more to bring to commercial fruition, evenafter the technical and economic feasibility ofthe substitute has been demonstrated. Govern-ment, industry, academia, professional soci-eties, and standard-setting organizations mayall play roles in this process, depending on thematerial and its application.

Substitution R&D relevant to strategic mate-rials is conducted in government, industrial,and academic laboratories. Since most of thesupport for this work has come from the gov-ernment, funding of the projects is subject toshifting governmental budgetary priorities andmay not be sustained for the protracted periodneeded to adequately demonstrate the techni-cal potential of a material or its application.Also, government conducted or sponsoredR&D can suffer from insufficient industrial in-terest in commercializing a material,

Industry, the group which ultimately decideswhether or not substitutes are adopted, usuallydoes not commit the funds, time, and effortnecessary to develop and qualify substitutes forstrategic materials unless such activities alsoprovide cost or performance advantages. Pri-vate firms often do not perceive national ma-terials availability and vulnerability as prob-lems that they have a major role in remedying,Availability concerns are usually not immedi-ate enough to cause much corporate concern.Table 7-2 illustrates the representative R&D pri-orities by government and industry.

Standard-setting and professional organiza-tions play key institutional roles in the devel-opment process by testing new materials anddeveloping standards for their use. Often, test-

266 . Strategic Materials: Technologies to Reduce U.S. Import Vulnerability

Table 7-2.—Primary Motivations for Substitution R&D

Industry GovernmentReduced import dependency . . . . . xCost advantage . . . . . . . . . . . . . . . . . xBetter performance . . . . . . . . . . . . . xNew market penetration . . . . . . . . . xMaterials conservation. ., . . . . . . . . xMaintenance of national

industrial competitiveness . . . . . xSOURCE: Office of Technology Assessment,

ing and standard-setting are done by volunteersfrom professional societies, with limited re-sources and time to dedicate to the effort. Inother instances, such as the qualification of anew superalloy for jet engine use, testing andqualification is undertaken by an individualfirm on a proprietary basis. The effort mayhave to be duplicated by others if the materialis to be used broadly. In many cases, severalyears of effort—and millions of dollars—maybe entailed in testing and qualifying a new ma-terial for use in a critical application.

Designer and End-User Acceptance

Acceptance by designers and end users canbe the highest hurdle in the adoption of a sub-stitute. These groups sometimes have been in-

different to the need to save strategic materi-als. A heightened awareness of the importanceof design to strategic materials vulnerabilitymay be able to reverse this indifference,

Substitutes are adopted only when compo-nent designers and end users have acquired ahigh degree of confidence in the technical ca-pabilities and economic potential of the newtechnologies. These materials users will not useany substitute technology with which they areuncomfortable; they are reluctant to makechanges, especially if the new designs orreplacement materials are relatively untried,Substitution in critical applications often re-quires a degree of confidence or comfort withthe new material or design that can only comefrom a proven track record. Consequently,promising substitutes are often introduced firstinto noncritical applications where confidencecan be gained without fear of catastrophicfailures.

These acceptance hurdles can be especiallyhigh for advanced materials. Since many ad-vanced materials are relatively recent develop-ments, they are still fighting to establish a trackrecord, This situation is exacerbated by the factthat most designers receive little formal train-ing in the use of advanced materials,

Summary of Substitution Prospects

On-the-shelf substitutes, which could beadopted by industry relatively quickly, enhanceU.S. preparedness to deal with import prob-lems. It has been estimated, for example, thatimmediately available substitutes could replaceone-third of the chromium now used. There arealso fully developed substitutes for cobalt andPGM in some applications. Substitution pros-pects for manganese are less promising, al-though substantial reductions in the amountof manganese needed per ton of steel producedare likely in the coming years because of theupgrading of steelmaking processes, as dis-cussed in chapter 6.

Industry response time depends in part onthe ready availability of information about sub-

stitute materials. Technologically sophisticatedfirms are generally aware of available substi-tutes, and some are reported to have under-taken contingency planning to address futuresupply availability problems. Less sophisticatedfirms may have greater difficulties in obtain-ing such information in the event of an actualsupply disruption, and, as a general rule, wouldhave the greatest difficulty in competing forscarce materials.

Substitution prospects in many critical eco-nomic and defense applications depends partlyon overcoming significant technical barriers.In these applications, substitutes must equalthe performance of the materials already used,which is often technically difficult, Substitutes

— —.. .—. . —

with low strategic material content have notyet been developed for some of these impor-tant applications. The degree of commitmentneeded to develop direct substitutes is substan-tial in both money and time. For applicationswhich require that alternative materials bequalified, the development effort may take 10or more years and several million dollars, evenafter their technical promise has been identi-fied in the laboratory.

Industry has little incentive to develop sub-stitutes on its own unless clear benefits in costor performance are anticipated. As a result, theFederal Government has undertaken or spon-sored most of the research where strategicmaterials savings, not cost or performance ben-efits, are given top priority. Several Federalagencies, including the Department of Energy(DOE), the Interior Department’s Bureau ofMines, and NASA have sponsored researchprograms aimed at developing substitutes forstrategic materials. However, the sustainedsupport needed to develop particular materialsto the point of commercialization generally hasbeen lacking,

Substitution research programs undertakenby NASA, the Bureau of Mines, and DOE na-tional laboratories have resulted in lower chro-mium research alloys that are potential substi-tutes for stainless steel in some applications.(Selected examples of these alloys are discussedin a subsequent section, and summarized in ta-ble 7-4,) Even if fully developed, most of thesematerials would not duplicate the great versa-tility of the high-volume stainless steels andwould be capable of replacing stainless steelsin only a limited range of applications.

With some exceptions, these substitutes areonly in the initial stages of development. Inmost instances, a continuing government com-mitment will be required if these materials areto be fully developed, since private industry isunlikely to undertake this research itself. Issuessurrounding possible additional Federal sup-port for such development activities are dis-cussed in chapter 8.

The Federal Government–especially NASA,through its Conservation of Strategic Aero-

Ch. 7—Substitution Alternatives for Strategic Materials ● 2 6 7

space Materials Program (COSAM)—has alsosponsored initial laboratory work on replace-ment superalloys that have reduced levels ofcobalt, These research materials could poten-tially reduce the cobalt now used in somenickel-based superalloys by one-half or more.However, full development of these replace-ment materials would require several moreyears and millions of dollars in additionalfunds. As with lower chromium stainless steel,subsequent development steps needed to bringthese substitute superalloy to the point of com-mercial use probably will need to be federallysupported if this development is to occur at all.

The changing material requirements of theaerospace industry may make it impractical todevelop these direct substitutes for superalloysto the point of commercial use. The develop-ment steps required could entail 5 to 10 yearsof additional effort. Beginning in the mid-1990s, advanced superalloy materials may be-gin to be commercially used in the next gen-eration of military aircraft. The direct substi-tutes now under development for currentlyused materials will not be suitable replace-ments for new materials used in the next gen-eration of jet engines. (Less near- and medium-term change in materials is expected in thecase of stainless steel.) Superalloy substitutionresearch is discussed in greater detail in a sub-sequent section.

In addition to direct substitutes, advancedmaterials (including ceramics and composites)are also under development because their prop-erties offer new possibilities in product designand performance. These materials, which con-tain little or no strategic metals, may have long-term implications for reducing import depen-dency, although to what extent is not clear. Be-cause the emphasis is on cost and performancebenefits, much of the development of advancedmaterials is carried out by private concerns.

Advanced ceramic materials have the poten-tial to displace metals where exceptional wear-resistance or heat-resistance is required. Cur-rent and prospective advanced ceramic appli-cations in which strategic materials are nowused are discussed in a subsequent section, and


summarized in table 7-II. Aerospace andautomotive applications command most of thefunds for ceramic R&D efforts.

Composites (including polymer matrix, metalmatrix, and carbon/carbon materials) are pri-marily under development because of theirlightness compared to conventional materials.In critical applications, their potential role inreducing strategic material requirements islikely to be indirect and will depend upon de-sign factors. At present, commercial applica-tions for advanced composites are dominatedby aerospace applications and high-value sport-ing goods. Increased use of composites in auto-motive applications is predicted.

Strategic materials conservation is not a pri-mary motivation in the development of ad-vanced materials, and the potential of thesematerials for displacing current requirements

for strategic materials should not be overem-phasized. Nonetheless, in the long term, theymay well bring fundamental changes in theoverall mix of materials in the domestic andinternational economy. Major industrial coun-tries including the United States, Japan, GreatBritain, and several Western European coun-tries are all vying for prospective markets forthese materials. Moreover, because of their keyimportance in defense applications, the ques-tion of the adequacy of domestic processing ca-pabilities with respect to these materials islikely to be an increasingly important issue.Processing capacity is often located in severaldifferent countries. The United States, for ex-ample, currently imports from Japan most ofits high-quality polyacrylonitrile (PAN) used asa precursor in carbon-carbon composites. Theinternational nature of these markets could cre-ate a new type of materials import dependency.

Prospects for Direct Substitution in Key Applications

Adequate substitutes exist for many applica-tions in which strategic materials are nowused. For example, aluminum alloys, plastics,and plated carbon steels already compete withstainless steels for many construction and con-sumer markets. In the event of a chromiumsupply disruption, these alternative materialswould be readily available as substitutes forstainless steel in many nonessential applica-tions where exceptional corrosion resistanceis not needed. Similarly, if the supplies of PGMwere to tighten, electronic components man-ufacturers could quickly substitute gold formuch of the platinum and palladium now usedfor contacts. This is a case where raw materialsprices are a significant part of the total prod-uct cost and can be counted on to drive sub-stitution. Fifteen years ago, gold was the pre-ferred material for contacts, but current pricesfavor platinum and palladium.

Materials substitution in many essential eco-nomic and defense uses is more difficult, how-ever. Performance compromises are very costlyin these cases, so the replacement must match

or better the properties of the current material,There are very few, if any, immediately avail-able replacement materials capable of meetingthe demanding performance standards requiredfor these applications. In some cases, adequatesubstitutes for the current materials have yetto be developed. In other cases, technicallyacceptable substitutes may be known, but aretoo expensive to be used. In still other cases,potential substitutes have been developed inthe laboratory but have yet to be taken throughthe time-consuming and expensive testingprocesses necessary to make them acceptablefor commercial use. Depending on the extentof the laboratory research and the promiseshown by the results, some of these substitutescould be brought to the point of commerciali-zation in the next 5 to 10 years, while othersare unlikely to be developed fully.

Chromium Substitution in Stainless Steel

Stainless steel accounts for almost half of thetotal U.S. chromium demand, and about 70 per-


cent of the chromium consumption in metal-lurgical uses. Table 7-3 shows the contributionof the highest volume stainless steel grades tochromium use. The most common grade, AISI304, alone accounts for over 40 percent of do-mestic stainless steel production and over 20percent of total domestic chromium consump-tion. Although the chromium content of stain-less steels varies from 10 to over 30 percent,on the average stainless steels contain about17 percent chromium.

The primary function of chromium in stain-less steel is to provide corrosion and oxidationresistance. z Chromium makes stainless steelhighly resistant to damage in a large variety ofenvironments. This characteristic, along withgood fabricability and mechanical properties,is what makes stainless steel so attractive fora wide variety of applications, ranging fromdecorative trim, kitchen utensils, and otherconsumer products to industrial applications

ZThe protection from corrosion and oxidation damage comesfrom the chromium oxide skin that forms at the surfaces of stain-less steels. Chromium concentrations of 12 percent or higherare required for the formation of the protective skin, but sincecorrosion and oxidation resistance increases with chromiumcontent, much greater concentrations are often used. AISI 304stainless steel contains 18 to 20 percent chromium, and somesuperstainless grades have chromium contents of 30 percent ormore.

In addition to conferring corrosion and oxidation resistance,chromium improves the hardenability and stabilizes the aus-tenite, the highly workable, ductile, and weldable microstruc-ture found in the majority of stainless steel grades.

such as tubing and reaction vessels in power-plants and chemical processing facilities.

There is little chance that a universal substi-tute for stainless steel can be found for use inall of these applications. However, some oppor-tunities exist for piecemeal substitution. Thepotential for reduced use of stainless steel (andthus chromium) in an emergency is very greatin the decorative and consumer uses and low-temperature (room temperature to 900

0 F) in-dustrial applications. Materials such as alumi-num, titanium, plastics, and low-chromiumstainless steels (9 to 12 percent chromium) canoften substitute without serious performancecompromises for stainless steels in these rela-tively undemanding uses. The possibilities forreplacement in the industrial applications oper-ating at higher than 900° F (5OO° C) is some-what smaller. In some of the moderately severe(referring to both temperature and corrosive-ness) industrial environments, steels with 12to 15 percent chromium would suffice wherehigh-chromium stainless grades (18 percent ormore) are now used. This substitution oppor-tunity exists because engineers often specifythe common grades, which have better prop-erties (and more chromium) than needed, in or-der to expedite the design process. In addition,there are low-chromium (e.g., 9 percent) orchromium-free steels now under developmentfor use in these moderately harsh environ-ments. Even considering these new alloys, re-

Table 7-3.—High-Volume Stainless Steels

Percent of domestic Percent of chromium Percent of totalstainless steel Typical chromium consumed in domest ic chromium

AISI stainless steel grade product ion compositions stainless steel consumption

301 . . . . . . . . . . . . . . . . . . . . 9.60/o 17.0% 9.4% 4.60/o304. . . . . . . . . . . . . . . ! . . . . 42.3 19.0 46.5 22.6304N & 304L . . . . . . . . . . . 4.0 19.0 4.4 2.1316. . . . . . . . . . . . . . . . . . . . 3.6 17.0 3.5 1.7316L . . . . . . . . . . . . . . . . . . 3.1 17.0 3.1 1.5

409. ......., ., . . . . . . . . 10.1 11.1 6.5 3.2430. ., . . . . . . . . . . . . . . . . . 3.5 17.0 3.4 1.6

Other grades . . . . . . . . . . . 23.9 NA 23.1 11.2

Total stainless ... . . . . . . 100.0 ”/0 17,3”/0 100.0 ”/0 48.50/oalncludes chromium in metal, ferroalloys, and chromiteColumns may not add to totals because of roundingNA = Not applicable, chromium composftlons vary greatly among these stainless steels

SOURCE American Iron and Steel Institute, Cwarfer/y Product/on of Stainless and Heat Res(stirrg Raw Steel, publication AlS-l04(1983) and U S Bureau of Mines, Miner-als Yearbook, Chromium Preprint (1982)


placement of the high-chromium stainlesssteels in extremely severe industrial applica-tions, especially those at temperatures above1,300° or 1,400° F (700° to 800° C) appears in-feasible. Much of this currently irreplaceabledemand for stainless steel is in critical defenseapplications, the chemical processing industry,and energy facilities such as powerplants andpetroleum and natural gas refineries. These ap-plications make full use of stainless steel’s im-pressive high-temperature corrosion and oxi-dation resistance and strength.

According to a 1978 report by the NationalMaterials Advisory Board (NMAB), in a sup-ply emergency 60 percent of the chromiumused in stainless steel could be saved throughthe use of low-or no-chromium substitutes thatare either already available or could be devel-oped within 10 years.3 The other 40 percent ofthe chromium consumed in stainless steel wasfound to be irreplaceable unless compensatedfor by design or process improvements. Thisamount represents approximately 20 percentof the current total domestic chromium use.

Most research on reducing the use of chro-mium in stainless steels is sponsored by Fed-eral agencies. The focus is on developing alter-native alloys with lower chromium contentsthan those stainless steels in greatest demand(e.g., AISI 304,409, and 301) for use in moder-ately harsh industrial environments. In addi-tion, R&D related to advanced surface treat-ment processes and ceramic and compositematerials, though not motivated by chromiumconservation, may uncover ways to reduce theuse of stainless steel in some applications,

Low-Chromium or Chromium-Free Substitutesfor Stainless Steels

Current commercial low-chromium steels areunsuitable as substitutes for stainless steel incritical applications. However, several low- orno-chromium alternatives for some grades of

3National Materials Advisory Board, Contingency Plans forChromium Utilization, National Research Council, Commissionon Sociotechnical Systems, Publication NMAB-335 [Washing-ton D. C.: National Academy Press, 1978).

stainless steel are under development (table 7-4.) These new steels show promise for variousmoderately harsh environments but do not per-form as well as high-chromium grades in ex-tremely severe applications. Most are still atthe laboratory stage of development, althoughsome are now undergoing certification, Thebulk of the research is being sponsored by Fed-eral agencies, since private firms have little in-centive at current chromium prices to developlow-chromium substitutes. (See ch. 3 for chro-mium price information.)

Low-chromium or chromium-free substitutealloys for the AISI 300 (austenitic) series stain-less steels have received the greatest attentionfrom researchers. Austenitic grades, most ofwhich contain between 16 and 26 percent chro-mium, account for nearly 70 percent of domes-tic stainless steel production and for about 36percent of all domestic chromium demand.Among this group is the very popular and ver-satile type 304. Excellent fabricability and me-chanical properties, combined with corrosionand oxidation resistance in a wide range ofenvironments, makes the 300 series stainlesssteels attractive for many applications, Unfor-tunately, the remarkable combination of prop-erties that enables this great versatility is cur-rently impossible to replicate, Consequently,a universal substitute for the entire 300 series(or even one of the particularly popular grades)is not a likely development, The promise ofeach of the substitutes tends to be very appli-cation- or environment-specific.

Examples of promising research on substi-tutes for 300 series stainless steels in moder-ately severe applications include:

● DOE’s Oak Ridge National Laboratory de-velopment and promotion of a modified 9percent chromium (Cr), 1 percent molyb-denum (Me) steel [modified 9Cr-lMo alloy).4

The initial objective of the laboratory wasto develop a single reference material forintermediate sections of liquid metal fastbreeder reactors, Currently, these reactorscontain 18 percent chromium-8 percent

4Basically a standard 9Cr-1Mo alloy with additions of colum-bium and vanadium.

—— . —.

Ch. 7—Substitution Alternatives for Strategic Materials • 271

Table 7“4.—Oevelopment Status of Potential Substitutes That Could Reduce ChromiumRequirements in Stainless Steel

Substitutematerial Key objective

1. Modified 9 % Develop single materialc hromium-1 % system to replacemolybdenum ferritic (2.25°/0 Cr)steel. and austenitic (18°/0

Cr) steels used inpressure vessels andconnecting tubing inliquid metal fastbreeder reactors.

2. 12°/0 chromiumalternative to18°/0 chromium304 stainlesssteel.

3. Iron aluminummolybdenum(Fe-8 °/O Al- 6°/o Mo)alloy strengthenedby zirconiumcarbide (ZrC).

4. 9°/0 chromiumaustenitic alloys.

5. Theoreticalmethod to de-velop low-chromium austen-itic stainlesssteel compo-sitions.

6. Manganese-alumi-num steel(Fe-M n-Al).

Determine feasibility ofreducing Cr use intype 304 stainless.

Develop chromium-freematerial for midtem-perature oxidation-resistant application.

Technicalstatus Institutional sponsors

Fully developed; may Oak Ridge Nationalalso find use in Laboratory.fossil, solar thermal,and fusion energysystems,

Determine if other alloy-ing elements couldreplace part of thechromium in stain-less steels.

Develop a technical toolfor devising low-chromium alloyswith mechanical pro-perties equivalent tothose of type 304stainless steel.

Develop general usealternative tochromium-nickelstainless steel.

Mechanical propertiesand corrosion andoxidation resistancecompare favorablywith type 304stainless.

Early tests show excel-lent workability andoxidation resistance,ZrC strengtheningmechanism couldnot be controlledreliably and needsadditional work.

Tests show corrosionresistance (in lesssevere environ-ments), fabricability,weldability, and me-chanical propertiescomparable to con-ventional stainlessgrades.

Modeling of alternativecompositions hasbeen undertaken. Notest heats have beenmade.

Laboratory work showsthat these alloysmay be useful atcryogenic and mod-erate temperaturesand various corrosiveenvironments.

NASA-Lewis ResearchCenter.

U.S. Bureau of MinesAlbany ResearchCenter.

INCO under U.S.Bureau of Minessponsorship.

Allegheny LudlumSteel Corp.

Studies are being con-ducted in many dif-ferent laboratories.

7. 6-12°/0 chromium Develop low-chromium Oxidation and creep ARMCO (producerferritic steels. oxidation-resistant resistance are super- company).

ferritic stainless ior to type 409steels. stainless.

Economic factorsand commercial statusIn process of certifica-

tion by ASME boil-er and pressurecode committee.Cheaper than18%Cr-8% Ni stain-less for indicateduses; lack of indus-try sponsorshipmay slow commer-cialization.

Laboratory stage;initial workcompleted in 1979.

Laboratory stage.

Laboratory stage.

Could add to thestockpile of infor-mation about sub-stitutes, but workhas yet to progressto the experimentalstage.

Most work is still atthe laboratorystage. Limited pro-totype testing isbeing done in othercountries. May becheaper than cur-rent stainlesssteels.

Laboratory stage.

SOURCE Off Ice of Technology Assessment

272 Ž Strategic Materials: Technologies to Reduce U.S. Import Vulnerability

●

nickel (Ni) (18 Cr-8Ni) alloys (e.g., AISI 304,321, 347) in the reactor vessels and heatexchangers and a 2¼Cr-1Mo alloy in thesteam generators. Use of a single materialin these applications eliminates, amongother problems, an undesirable dissimilarmetal weld at the transition joints. Themodified 9Cr-1Mo alloy was found to bea promising replacement for both types ofmaterials. The encouraging results of theresearch suggest that this alloy may finduse in conventional power applications, aswell. Although it will replace both low- andhigh-chromium materials, modified 9Cr-1Mo will probably yield a net chromiumsavings. However, chromium conserva-tion is a byproduct of this development ef-fort, not a primary motivation. If this newmaterial sees widespread use in the powerindustry, the resultant availability anddesigner acceptance may encourage its usein other low or moderately hostile appli-cations now dominated by high-chromiummaterials.

Nearing commercialization, this modi-fied 9Cr-1Mo alloy is being considered bythe American Society for Testing of Ma-terials (ASTM) and by the American So-ciety of Mechanical Engineers (ASME)boiler and pressure vessel code commit-tee for final certification. Since use of thematerial entails fabrication and inspectioncost savings, as well as a materials cost re-duction, prospects for successful substitu-tion are good if it is approved5 6 (table 7-4,item 1).NASA’s comparison of the mechanicalproperties and oxidation and corrosion re-sistance of reduced chromium alloys withthose of type 304. One steel, containing 12percent chromium, 10 percent nickel, 1.5percent silicon, 1 percent aluminum (Al),2 percent molybdenum, and 2 percentmanganese (Mn), demonstrated propertiesthat compare favorably with 304 stainless

‘Robert R. Irving, “What’s This Steel They’re Raving AboutDown in Tennessee?” Iron Age, June 25, 1982,

‘V. K. Sikka and P. Patriarca, Data Package for Modi~ied 9Cr-IMO Alloy [Oak Ridge, TN: Oak Ridge National Laboratory, De-cember 1983).

●

●

●

steel and could be used for most applica-tions (except nitric acid environments)where type 304 is currently used. This al-loy conserves one-third of the chromiumnormally used in type 304 stainless steel7

(table 7-4, item 2).The U.S. Bureau of Mines’ investigation ofa chromium-free iron-aluminum-molybde-num (Fe-Al-Mo) alloy as a potential substi-tute for high-chromium, heat-resistant al-loys. An optimal composition for the alloyhas yet to be developed, but early findingssuggest that the chromium-free alloy mayresist oxidation at moderate temperaturesto an extent comparable to 300 series stain-less89 (table 7-4, item 3).The Bureau of Mines’ work on reduced-chromium substitutes for high-performancestainless steels (e.g., type 310 with 25 per-cent chromium) used in elevated-temper-ature, severely corrosive environments,Steels containing chromium (12 to 17 per-cent), nickel, and aluminum are beingstudied in this program. The Albany Re-search Center of the Bureau of Mines hasbeen successful in reducing the chromiumcontent to 12 percent. One 12 percentchromium substitute has about three timesthe sulfidation-resistance of, and approx-imately equivalent mechanical propertiesto type 310 stainless steel.10

The Bureau of Mines’ study of low-chromi-um stainless steels for high-temperature,oxidation-resistant applications. Researchhas shown that steels having 8 to 12 per-cent chromium with additions of alumi-num and silicon can have excellent oxida-tion-resistance and mechanical properties(to 800° C), These alloys are potential sub-stitutes for 18Cr-8Ni stainless steels in————

7Joseph R. Stephens, Charles A, Barrett, and Charles A.Gyorgak, “Mechanical Properties and Oxidation and CorrosionResistance of Reduced-Chromium 304 Stainless Steel Alloy s,”NASA Technical Paper 1557, November 1979.

‘J. S. Dunning, An iron-Aluminum-Molybdenum Alloy as aChromium-Free Stainless Steel Substitute, U.S. Department of theInterior, Bureau of Mines Report of Investigations 8654 (Wash-ington, DC: U.S. Government Printing Office, 1982).

‘J. S. Dunning, M. L. Glenn, and H. W. Leavenworth, “Sub-stitutes for Chromium in Stainless Steel s,” Metal Progress,October 1984, p. 23.

l’JIbid., p. 23.


some applications. Further long-range re-search to qualify other important proper-ties such as high-temperature stability,weldability, and age-hardening character-istics is underway .11

● Research sponsored by the Bureau of M i n e sat the Inco Alloy Products Research Centeraimed at replacing some of the chromiumnow needed for stainless steels used in cor-rosive environments. The findings suggestthat it may be feasible, with additions ofnickel, molybdenum, copper, and vana-dium, to produce 9 percent chromiumaustenitic stainless steels with corrosionresistance, hot working behavior, weldabil-ity, and mechanical properties compara-ble to those of conventional grades. Theselow-chromium alloys, while not adequatefor more severe environments, could beused in decorative, aqueous, and some in-dustrial applications” (table 7-4 item 3).

● Allegheny Ludlum Steel Corp. ResearchCenter’s development of a theoretical mod-el for devising new reduced chromium al-

loys that would duplicate the excellent me-chanical properties of type 304 stainlesssteel, although not its corrosion resistance.Actual alloys have not been developedfrom these theoretical compositions,which range from 6 to 16 percent chromi-um, but some of them could be suitable assubstitutes in noncritical applications13 (ta-ble 7-4 item 5).

• Various researchers’ work with iron-man-ganese-aluminum (Fe-Mn-Al) steels. The Fe-Mn-Al steels contain no chromium, butmay consist of up to one-third manganese,another strategic material. The high alu-minum content of the Fe-Mn-Al steels pro-vides oxidation resistance, Though mostof the work is still preliminary, these alloysshow promise as replacements for 300 ser-ies (chromium-nickel) stainless steels insome moderately corrosive environments.

‘l Ibid., p. 23.‘2S. Floreen, “An Examination of Chromium Substitution in

Stainless Steels, ” Metallurgical Transactions A, November 1982.13R. A. Lula, ‘‘Potential Areas for Chromium Conservation in

Stainless Steels, ” in Technical Aspects of Critical Materials Useby the Steel Industry, vol. 11A, NBSIR 83-2679-2 (Washington,DC: U.S. Government Printing Office, June 1983).

Photo credit US. Department of the Interior, Bureau of Mines

An 80-pound heat of an experimental low-chromiumstainless steel is poured into a split steel mold at the

Bureau of Mines, Albany Research Center

With heat treatment, the Fe-Mn-Al steelsdemonstrate excellent mechanical proper-ties, in some cases as good as or better thantype 304. In addition, they are 10 percentlighter (and have greater strength-to-weightratios) than nickel-chromium stainlesssteels, Though the economics depend onthe relative costs of manganese, alumi-num, chromium, and nickel and the sizeof the production runs, Fe-Mn-Al alloysare likely to be less costly than 300 seriesgrades 14 15 (table 7-4, item 6).

14 Samir K. Banerji, “The 1982 Status Report on Fe-Mn-AlSteels, ” as cited in Technical Aspects of Critical Materials Useby the SteeI Industry, ” vol. IIB, NBSIR 83-2679-2, June 1983.

1’Rosie Wang, “New Stainless Alloy is Less Costly, ” Ameri-can Metal Market, Sept. 19, 1983,


Information requirements for stainless steelsubstitutes are under evaluation by the MetalProperties Council, Inc. (MPC), an organiza-tion set up by industry and technical societiesin 1966 to provide engineering data on mate-rials, MPC established a Task Group on Criti-cal Materials Substitution in 1981. An initialMPC task group report,16 issued in 1983, noteda gap on the technical information about alter-native low-chromium compositions for stain-less steel. Most of the available data was fromlaboratory investigations, with little informa-tion developed about processing and fabrica-tion of these compositions, or about how theyheld up in service environments—essentialinformation if industry were to use these sub-stitutes during a protracted supply shortage.Subsequently, MPC has decided to focus onchromium substitution options for 18 percentchromium-8 percent nickel stainless steels usedin room-temperature to moderately high-tem-perature (up to 1,2000 F) applications.17 Theseapplications comprise the highest volume usesfor stainless steels, including many for whicha decrease in corrosion resistance may be ac-ceptable to some consumers in times of a sup-ply shortage. MPC is now evaluating futuresteps, such as developing alternative compo-sitions that duplicate all metallurgical and me-chanical properties of the popular grades ofsteel, except corrosion resistance. MPC is pre-paring a survey to gain input from industry.

The AISI 400 series, accounting for about 20percent of domestic stainless steel production,is the second largest class of stainless steels.Type 409, which contains approximately 11percent chromium, is the second most popu-lar stainless steel. It accounts for about half theproduction of 400 series grades and is usedprincipally in the catalytic converter housingsin automotive exhaust systems.

ARMCO is exploring several lower chromiumalternatives to ferritic (400 series) stainless steelscontaining 12 percent chromium, These newalloys, still at the laboratory stage, may be prom-—. .- ——-.——

leThe Meta] Properties Council, Inc., “Task Group on Critica]Materials” (New York: The Metal Properties Council, Inc., 1983).

ITprivate communication with R. A. Lula and officials of theMPC.

ising substitutes for stainless steel used in thecatalytic converter shell of automobiles, ARMCOreports that its 6.6 percent chromium alloy 6SR(scale resistant) is more oxidation- and creep-resistant than 409 stainless steel. Unlike, the othersubstitutes described above, the SR alloys (whichalso include 12SR, a potential 12 percent chro-mium substitute for some 18 percent chromiumgrades) are being researched in the producer in-dustry. As a result, the institutional barriers tothe acceptance of these SR alloys are relativelylow 18 (table 7-4, item 7),

These substitutes are all in various stages of de-velopment. Other than the modified 9Cr-1Mo al-loy, which is undergoing certification, thereplacement alloys have not yet advanced beyondthe laboratory level of investigation in the UnitedStates. The development of the chromium-freesubstitutes, such as the ferritic Fe-Al-Mo and theaustenitic Fe-Mn-Al alloys, designed for ele-vated-temperature oxidation/corrosion-resistantservice, probably involve the longest range, high-est risk research. The low-chromium alloys alsorequire additional study, but technical successis in general less speculative, Extensive addi-tional testing of mechanical properties, phase sta-bility, and other physical properties of any of thenewly designed alloys, as well as ease of proc-essing, could take several years. Even if these al-loys overcome the initial hurdles, economic fea-sibility will remain in question. Without largemarkets in place, these alloys cannot be producedcheaply enough (due to poor economies of scale)to compete effectively with the current high-volume stainless steel products.

Advanced Surface TreatmentTechnologies and Processes

Most of the chromium in stainless steel ispresent solely for corrosion and oxidation re-sistance. Chromium’s secondary roles can bemet with the use of other alloying elements orprocessing techniques. Since corrosion and ox-idation resistance is only needed at the surface,the chromium on the interior of the stainless—.—

leJoSeph A. Douthett, “Substitute Stainless Steels With LessChromium, ” in Conservation and Substitution Technology forCritical Materials, vol. I, NBSIR 82-2495 (Springfield, VA: Na-tional Technical Information Service, April 1982).

Ch. 7—Substitution Alternatives for Strategic Materials . 275.— .

steel is nonessential, Surface modification tech-niques can endow low- or no-chromium ma-terials with corrosion and oxidation resistancesufficient to substitute for stainless steels insome applications, Advanced surface treat-ment techniques may also improve wear resis-tance, thus extending product life.

Existing fully developed surface treatmenttechnologies—e.g., plating steels with chro-mium, nickel, cadmium, or zinc or welding astainless steel overlay to nonchromium alloys—have been used for decades in a large numberof applications, but there are constraints intheir use. Fabricated parts and brittle metalscannot be clad, for example, and clad materialsare difficult to weld. Claddings sometimes sep-arate from the base metal, with potentially dis-astrous results.

A number of advanced processes now underdevelopment or in the early stages of commer-cialization may broaden applications for sur-face treatment. One advanced coating tech-nique that can compete directly with stainlesssteels in some applications is the DILEX proc-ess, This technique involves the diffusion ofchromium (or other elements) into the surfaceof a ferrous part that is placed in a lead bath.The surface alloy typically contains 25 percentor more chromium (and possesses excellentcorrosion and oxidation resistance), while theunderlying substrate contains little chromium.The cost of continuously processed DILEXstrips is currently competitive with stainlesssteel products. In addition, parts and compo-nents that are difficult to fabricate from stain-less steel can sometimes be produced moreeasily with the DILEX process.19

Surface alloying with lasers (by processescommonly referred to by their United Technol-ogies trade names, LASERGLAZING andLAYERGLAZING) can provide corrosion andoxidation protection and wear resistance tomaterials. LASERGLAZING can improve ero-sion and corrosion properties through elimi-

~eRa}l J, L’a n Th~’n e, “Conservation of Critical Metals Utiliz-ing Su~face Alloy ing, ’ ‘as cited in Conser~ration and SubstitutionTmhnoIogj for CriticaJ ,MateriaJs, v~l. II, NBSIR 82-2495 April1982.

nation of surface porosity, and can produce awear-resistant surface that could extend the lifeof steels used in metal cutting and grinding.LAYERGLAZING can be used to build entireparts (e. g., turbine discs) through continuousmelting of very thin layers of alloy at the sur-face. Such processes permit tight control overthe composition of the alloy and can also re-duce part rejections, since flaws detected inprocessing can be reglazed immediately. Whilelaser techniques have impressive capabilities,these processes are not presently as cost effec-tive as some of the more established surfacemodification practices, such as roll bonding.

A recent technological advance, ion implan-tation, holds long-term promise as a way of im-proving the wear- and corrosion-resistance ofparts, thus helping conserve strategic materialsthrough extending product life or reducing theneed for chromium in corrosion-resistant ap-plications. In ion implantation, high-energyions of alloying elements are embedded intothe surface of the workpiece to produce a sur-face layer of 100 to 1,000 angstroms that is anintegral part of the substrate. Advantages ofthis technique include excellent coating-sub-strate adhesion (owing to the lack of a sharpboundary between the two), no dimensional al-teration of the substrate, and low processingtemperatures. Elements such as carbon, nitro-gen, chromium, and nickel can be implanted,but the resulting properties are not as depen-dent on the type of ion as on the mechanicaldeformation it causes to the matrix surface.Therefore, the choice of an ion is based on itsmechanical effect in the host material, noton its own inherent corrosion- or oxidation-resistant properties. 20

Ion implantation has been shown to extendthe life of cobalt-based cemented carbides andtool steels when carbon and/or nitrogen are ap-plied. Implantation of yttrium in diesel fuel in-jection pumps reportedly dramatically im-proves wear resistance in comparison withchrome plating. Bureau of Mines-supported re-search has shown that ion implantation can

Zochar]es River Associates, INeIIF Metals Processing Technol-

ogies, OTA contract report, December 1983, p. 46.


protect plain carbon steels against mild aque-ous corrosion.

Ion implantation techniques, first developedin Great Britain, are fully commercialized inthe semiconductor industry. For metallurgicalapplications, ion implantation is at the opera-tional prototype stage—commercial machinesare being developed, but there has been littlemarket penetration.21 Substantial technical andeconomic constraints impede its use for large-volume metallurgical uses. To be effective inproviding corrosion resistance, ionic densitymust be much greater than in semiconductorapplications. Commercial equipment capableof handling this higher beam density has yetto be developed and appears to be prohibitivelyexpensive at this time. High capital costs andlimited product size and production rates arekey constraints acting against this technique’swidespread use.

All surface treatment techniques have draw-backs, If the surface layer fails, the exposedsubstrate would be vulnerable to corrosion.Fabrication and construction with surface-treated materials is more difficult and costlythan with monolithic materials. Special weld-ing and joining techniques must be used to as-sure that the base material does not become ex-posed, Edges of the material must be treatedto maintain protection. These welding and join-ing techniques are subject to separate researchand development efforts. In addition, surfacetreatment can be very expensive, so there aremajor efforts aimed at improving the processeconomics of these techniques.

Surface treatments also face nontechnicaland noneconomic hurdles, Designers and con-sumers often resist use of surface modificationprocesses in new applications where solidmonolithic alloys perform satisfactorily.

ZICarnegie-Mellon university, Department of Engineering andPublic Policy, Department of Social Sciences, and School ofUrban and Public Affairs, The Potential of Surface TreatmentTechnologies in Reducing U.S. Vulnerability to Strategic Materials,Pittsburgh, PA, April 1984.

Chromium Substitution in Alloy Steels

About 15 percent of U.S. metallurgical chro-mium (10 percent of total domestic chromium)is consumed in alloy steels, Chromium is usedin these steels primarily as a hardening agent.Although other elements, such as molybde-num, silicon, and nickel, can be used for thispurpose, chromium and manganese are cur-rently the most cost-effective hardenability en-hancers, Because chromium’s hardenabilitycharacteristics are more easily replicated thanits corrosion and oxidation attributes, fewertechnical problems exist in developing ade-quate substitutes for alloy steels than for stain-less steels. In its 1978 Chromium Utilizationstudy, the NMAB concluded that 80 percentof the chromium used in alloy steels could bereplaced either now or after a short-term R&Deffort.

The chromium contents of alloy steels typi-cally range from less than 1 to 4 percent, al-though some grades have as much as 9 percent.Compared to carbon steels, these steels haveimproved strength, wear resistance, and hard-enability. They are chosen when parts (e.g.,bearings, gears, shafts) will be highly stressedover a long service life.

Several alternative chromium-free alloy com-positions are under investigation as substitutesfor large-volume alloy steels. These alloys havebeen designed to duplicate the most importantproperties of the steels they would replace, sothat processing changes and design changescould be minimized if they were to be used asreplacement steels.

Work at the International Harvester Co.,sponsored by the Bureau of Mines, was aimedat the design of chromium-free substitutes fortwo alloy steels that together account for about60 percent of the chromium used in construc-tional alloys, or about 6 percent of total U.S.chromium demand. These Cr-Mo grades (AISI4100 series) and the Ni-Cr-Mo grades (8600 ser-ies) have been used for decades, and as a re-sult, current designs for parts and manufactur-ing processes are adapted to these steels. Thechromium in these grades was substituted with


manganese, molybdenum, and nickel. Silicon,another common hardening agent, was notused because alloy steel producers have littleexperience with the high silicon levels (0,6 per-cent Si) required to achieve the desiredhardenability. The compositions of the Mn-Ni-Mo and Mn-Mo replacement steels are shownin table 7-5.

To minimize the disruption entailed in shift-ing to new steels, the new chromium-free steelswere designed to be produced using prevalentU.S. production practices. Moreover, the ex-perimental substitutes have the same micro-structure, heat treatment response, and me-chanical properties as the steels they wouldreplace, and therefore would provide equiva-lent engineering performance. So far, actualproduction of these steels has been limited to100-pound” experimental test heats, thus thesteels’ characteristics in large-scale commer-cial production have not been demonstrated.

The second phase of this program—to pro-duce larger heats for testing–was delayed,owing to the financial status of the contractor.However, in 1984 the Bureau released a requestfor proposal which calls for about a 3,000-pound test heat. When completed, this phaseof the program will provide better informationfor the possible transfer of this technology toindustry.

In the original economic analysis (based on1981 raw materials costs), these steels were notfound to be cost effective. However, the Mn-Mo replacement for the 8600 series steels maybecome economical with the moderate chro-

mium price increases that would be expectedunder steady economic and political condi-tions. The other replacements (Mn-Ni-Mo for8600 and both Mn-Ni-Mo and Mn-Mo for 4100)would become economical only with the dras-tic price increases (on the order of tenfold forchromium ore and fourfold for ferrochromium)that would accompany severe chromium sup-ply disruptions, such as a complete cutoff fromSouth African supplies. To facilitate their usein such an emergency, the researchers recom-mended additional testing of these steels to de-termine equivalency of these steels under typi-cal production practices by U.S. producers .22

Development of these alternative steels wasfacilitated through International Harvester’sCHAT (Computer Harmonizing ApplicationsTailored) system, which first identifies metal-lurgical properties needed for particular partsand then selects the least-cost alternatives fromAISI and SAE steels that are available. Use ofcomputerized information systems of this sortcould facilitate the development of a strategicmaterials substitution information system thatcould be used in an emergency.

Reducing Cobalt and Chromium Used inSuperalloy for High-Temperature Applications

Superalloys, used in jet engines, industrialgas turbines, and a widening spectrum of otherindustrial applications, account for 30 to 40

Zzcar] J. Keith and V. K. Sharma, Development of Chromiu m-FreeGrades of Constructional Alloy SteeJs, U.S. Department of the In-terior, Bureau of Mines’ contract No. JO1 13104, May 1983.

Table 7-5.—Ladle Analysis Ranges for the Chrome-Free Replacement Compositions forStandard 4118 and 8620 Steels (in percent)

4100 type steel 8600 type steel

AISI-4118 Mn-Ni-Mo Mn-Mo AISI-8620 Mn-Ni-Mo Mn-MoChemistry ladle range steel replacement replacement steel replacement replacement

Carbon. . . . . . . . . . . . . . . . . . 0.18-0.23 0.16-0.21 0.16-0.21 0.18-0.23 0.16-0.21 0.16-0.21Manganese . . . . . . . . . . . . . . 0.70 0.90 1.00-1.30 0.70-0.90 1.00-1.30 1.00-1.30Chromium . . . . . . . . . . . . . . . 0.40-0.60 rNickel . . . . . . . . . . . . . . . . .

0.08-0.15 0.15-0.25 0.25-0.35 0.15-0.25 0.25-0.35 0.35-0.45r— residualsilicon range = 0, 15-().35°/0, sulfur = O 05°/0 maximum, phosphorus = 0.04°/0 max!mum

SOURCE Carl J. Keith and V K Sharma, Deve/oprnerrt of Chromium-Free Grades of Constructfona/ A//oy Stee/s, U S. Bureau of Mines contract No JO1 13104, May 1983


percent of U.S. cobalt consumption. Only asmall portion of U.S. chromium consumptiongoes into superalloys—about 3 percent in 1982.This amount is in the form of highly purifiedferrochromium and chromium metal. Othermaterials used in superalloys include nickel,aluminum, titanium, and a number of minoralloying elements, including columbium (nio-bium) and tantalum—two second-tier strategicmaterials for which the United States is import-dependent.

While many superalloys do not contain co-balt, the use of cobalt has increased over timebecause it improves the weldability of some su-peralloys, contributes to their strength, and alsoenhances oxidation and corrosion resistance.Chromium is currently essential in all super-alloy.

Importance of Superalloy to the Aerospace Industry

Improved jet engine performance has beenhighly dependent on development of newsuperalloys 23 that extend the maximum oper-ating temperature of the engine yet are still ableto withstand the high mechanical and thermalstress, oxidation, and hot corrosion that occursin the hot section parts of a jet engine. Throughcomplex adjustments in composition and proc-essing, the temperature capability of super-alloy has been extended from about 1,4000 Fin 1940 to about 1,9500 F today (some superal-loys now in use have operating temperaturesof about 2,100° F), as shown in figure 7-1. Inaddition, the required life of various compo-nents (the minimum predictable time beforeoverhaul or replacement) has also increasedsignificant y.

ZsThe ana]ysis of superalloy substitution potential in this sec-tion is drawn in large part from Richard C. H. Parkinson, Sub-stitution for Cobalt and Chromium in the Aircra-ft Gas TurbineEngine, OTA staff background paper, September 1983. It shouldbe noted that superalloy use is spreading to many nonaerospaceapplications, such as oil country tubulars, heavy duty tooling,pulp and paper production, medical and dental uses, and glassmanufacture. In these applications, superalloy were substitutedfor other materials that could again be used in an emergency,although possibly with some performance costs. In the case ofgas turbine engines used in jet aircraft, however, alternativesto superalloy are not currently available, and moreover are notlikely to be developed in this century. Thus, aerospace uses re-main the most demanding and critical superalloy applications.

Each individual component in the hot sec-tion of a jet engine, such as turbine blades,vanes, and discs, requires a superalloy with adifferent range of properties—so that develop-ment of an adequate substitute for one partdoes not mean that it can also substitute forother parts, In addition, each of the U.S. jet en-gine manufacturers maintain separate speci-fications for superalloy that can be used ineach part. Today, there are well over 100 su-peralloys used domestically, but some of thesemay be certified for use only by one enginemanufacturer, Table 7-6 shows representativesuperalloys used in the different parts of thehot sections of current jet engines,

As superalloy have become more special-ized, their costs have escalated, so that it oftentakes a decade or more and several million dol-lars to bring a promising new alloy even to theengine testing stage. Initial development of anew superalloy in the laboratory for disc orblade applications constitutes only part of thetotal effort. Prior to engine qualification anduse, a complete design data base, specificationsand standards, component and machine test-ing, and commercial-scale heats must be dem-onstrated, Without a pressing need for substi-tutes, industry alone is unlikely to make thiskind of commitment.

Substitution Prospects

From the standpoint of reducing U.S. vulner-ability, backing out or reducing cobalt andchromium use in superalloy would be highlydesirable–but only if they could be achievedwithout impairing the push toward higher per-formance in military applications. Continuedincrease in performance is the primary objec-tive behind most government and industrial re-search aimed at developing new hot-sectionmaterials, although many of these materialscould have the side benefit of reducing strate-gic materials requirements. Figure 7-2 showsNASA estimates of the approximate date forintroduction of some of these higher tempera-ture materials in aircraft. These materials arediscussed later in this chapter.

Superalloys will almost certainly remain theprimary structural material in turbine blades

Ch. 7—Substitution Alternatives for Strategic Materials . 279

for at least

Figure 7-1 .—Temperature Capability of Superalloy2,000

1,500

1.4001940 1950 1960 1970 1980

Approximate year availableSOURCE Garrett Turbine Engrne Co

the next 20 to 30 years. During thisperiod, complete elimination of cobalt andchromium in jet engines is highly unlikely, al-though use of alternate alloys, wider use ofcoatings, and adoption of more efficient proc-essing technologies could reduce use of thesematerials in individual applications.

In the long term, probably not before the sec-ond decade of the next century, a variety ofnonmetallic materials (e. g., advanced ceram-ics and carbon-carbon composites) may be de-veloped sufficiently to be widely used in somehot-section parts of human-rated jet engines.If so, chromium, cobalt, and other metals thenmay begin to be phased out of jet engines. Ac-tual production dates for the first engines con-taining significant amounts of nonmetallic ma-terials is likely to be well beyond the year 2000.

In the sections that follow, near-term (to1990), medium-term (1990 to 2000), and long-term prospects for reduced chromium and co-balt usage in jet engines are selectively dis-cussed, under the assumption that R&D effortscontinue at approximately their present levels.Institutional factors that could affect the extentto which various substitution potentials areadopted are discussed in the concluding sec-tion of this chapter.

Near-Term Prospects for Cobalt Substitution (to 1990)

Cobalt supply insecurities in the late 1970sled U.S. jet engine makers to substitute alreadydeveloped nickel-base superalloy for cobalt-base alloys wherever possible. A conspicuousexample of this was the substitution of the al-ready developed and qualified cobalt-free su-peralloy Inconel 718 for Waspaloy (13 percentcobalt) in turbine disk applications below 7000C. Inconel 718, which contains a large amountof niobium, a strategic material importedlargely from Brazil, continues to be used inthese applications owing to its comparativecheapness and ease of fabrication. Other super-alloy substitutions included replacement ofcobalt-base vanes with cobalt-free nickel-basesuperalloy.

Cobalt prices are unlikely to stimulate fur-ther substitution in the near term. Easy to ac-complish substitutions have already takenplace, As a practical matter, adoption of lowerchromium or cobalt substitutes by enginemakers is not likely unless substantial improve-ments in properties, higher temperature capa-bilities, or ease in fabrication accrue, as well.

Processing Advances. —As a result, the greatestopportunities for cobalt and chromium conser-


Table 7-6.—Typical Structural Alloys Used for Hot-Section Components

Nominal operating conditions

Composition (percent weight)Surface

temperatureComponent Alloy Ni co Cr Fe Form Stress (oF)

Combuster liner . . . . Hastelloy XHA-188

Turb ine va lve MA-754MAR-M 200MAR-M 247

MAR-M509X-40IN-713Rene-77

T u r b i n e b l a d e Alloy 454

MAR-M200MAR-M247B-1900Rene-80IN-713LCRene-77

Turbine disc. IN-100MERL-76Astroloy

WaspaloyRene-95IN-718IN-901A-286

C a s e WaspaloyIN-718IN-901A-286

4822

786060

101 0 572.555

62.560606560.572.355

5654.155.5

5861.3534525.5

58534525.5

1 541

—1010

5556—15

51010109 5

—15

18,518,517

13,59

———

13.5———

2222

2098

23.525.513.515

10988

141215

12.512.415

19.5141912.515

19,51912.515

18.5—

1——

————

,.

cccccccc

–Large grains–— se——————

———

——183455

—183455

DSCC, DSDScccccc

–Small grains–PM +HIP, PM +forgedPM +HIP, PM +forgedPM +HIP, PM +forged,

forgedForgedPM +forgedForgedForgedForged–Small grains–Sheet, forgedSheet, CC, forgedForgedForged

LowLow

Moderate10 low

High

1600

16001600

1900+ ‘1900

1800-1850

1800 +1800 +

16001600

19001850

1800-1850180017501600

–Rim temperature–130013001300

1250High 1200

120011001000

1300High 1200

11001000

vation in superalloys in the near term lie incontinued commercialization of advancedprocessing technologies, which have the in-cidental effect of improving cobalt or chro-mium yields in parts or of extending the lifeof components.

Several of these new metals processing tech-nologies are currently being adopted by indus-try, as is discussed in chapter 6. Powder metal-lurgy, with its potential to produce parts that

are close to their final shape, can dramaticallyreduce reject rates and scrap generation infabrication of engine components. Two powdermetallurgy processes used in conjunction witheach other—hot isostatic pressing (HIP) andisothermal forging—are now used commer-cially, although equipment costs are high.

Improved material utilization would beachieved if HIP parts did not have to be hotworked. This is now essential in order to over-

——.


Figure 7-2.— Temperature Capabilities of Turbine Blade Materials

800

SOURCE’ National Aeronautics and Space Administration

come fatigue problems, but reduces productyields. The U.S. Air Force Office of ScientificResearch is supporting research in this area toimprove the final quality of superalloy com-ponents.

Hot isostatic pressing can also be used to re-juvenate turbine vanes and blades, potentiallydoubling the operating life of parts. So far, HIPrejuvenation has been used primarily in indus-trial gas turbines but is not yet widely used forworn aircraft parts. As discussed in chapter 6,life cycle extension techniques are under in-tensive investigation by the Air Force, andsome jet engine parts are now being saved(rather than sold as scrap), pending possible im-provements in rejuvenation technologies. Mostobsolete jet engine parts, however, continue tobe sold as scrap, and most of the scrap is down-graded to less demanding uses.

By the end of the 1980s, additional jet engineapplications for cobalt-free oxide dispersionstrengthened (ODS) superalloy are probable.These nickel- and iron-based superalloys areproduced through a mechanical alloying proc-

ess, first developed in 1968. Although still con-sidered an emerging technology, rapid growthin ODS production is expected as new appli-cations are accepted.

All currently available ODS superalloys arecobalt free and are marketed by the Inco Al-loy Products Co. One ODS alloy, MA-754, hasbeen used for years in high-pressure turbinevanes of military aircraft produced by GeneralElectric. New applications for ODS alloys incombustor linings and turbine blades are beinginvestigated as part of NASA’s Materials forAdvanced Turbine Engine [MATE) Program.

NASA and Pratt & Whitney Aircraft are cur-rently evaluating another cobalt-free ODS alloy(MA-956) for use in combustor linings. Earlyresults suggest that MA 956, coupled with de-sign changes, could extend the operational lifeof these linings by up to four times comparedto existing linings. It can also be used at ahigher temperature than a commonly usedliner material, Hastelloy X (which contains 1.5percent cobalt).

38-844 0 - 85 - 10 , QL 3


Although ODS alloys are superior at hightemperatures (i.e., 2,100° F), their poorer per-formance in intermediate temperature ranges(i.e., 1,4000 to 1,600° F) has so far preventedtheir use in turbine blades. However, NASA,in conjunction with the Garrett Turbine EngineCo., is evaluating the recently developed cobalt-free ODS alloy MA-6000, for turbine blade ap-plications. Research suggests that an increasein surface metal temperature of 1500 F over thebest current superalloy blade material may befeasible.

ODS alloys are more expensive than conven-tional superalloy. With expanded markets,however, finished part costs have declined. Ad-ditional price reductions could arise if the mar-ket expands into turbine blade and industrialapplications. Current production of these al-loys is about 120,000 pounds per year, but isgrowing rapidly.

Coatings.—Continuing near-term progress inenhancing the surface properties of hot-sectioncomponents through use of coatings is also ex-pected. Coatings of one sort or another havebeen used since the 1960s and have extendedthe life of parts significantly. Thermal barriercoatings (TBCs), now used on combustor lin-ings and vane platforms, provide oxidation andhot corrosion resistance through a metallicbond coat (often containing chromium), which,in turn, is covered with a thin ceramic coat toprovide thermal insulation. TBCs have yet tobe applied to turbine airfoil surfaces becausepeeling problems have not been completelyovercome. However, they may may be used onairfoil surfaces by the end of the decade.

Coatings (or other surface treatments) maysome day permit reduced use of chromium insuperalloys—although near-term prospects arevery limited. Chromium’s primary function insuperalloy is to provide oxidation and hot-corrosion resistance at the surface of compo-nents. Most superalloy contain several timesas much chromium as strictly needed to pro-vide this surface protection. As an insurancemeasure, chromium is added throughout thealloy, even though it is only needed at thesurface.

Aside from its absolutely essential role in cor-rosion resistance, the high levels of chromiumthroughout monolithic superalloy may not beneeded. In theory, conservation of chromiumand improved mechanical properties could beachieved if a safe way could be found to putchromium only at the surface of components,leaving the rest of the part chromium free. Pres-ently, coating or cladding of a chromium-freebase alloy is not acceptable, owing to the pos-sibility of a disastrous crack forming in thecoating. Other advanced surface treatmentprocesses have yet to be applied for the spe-cific purpose of reducing chromium content.

From the above discussion it would appearthat prospects for cobalt substitution in super-alloy are quite limited in the near term, andthat few available alternatives are ready for useby engine manufacturers, Chromium substitu-tion prospects are even more limited.

Medium-Term Prospects for Further Cobalt andChromium Substitution (1990-2000)

Over the next 10 to 15 years, only substitutematerials that are now approaching qualifica-tion and approval for jet engine use are likelyto be useful in reducing U.S. dependency onimported strategic materials, The long leadtime entailed in testing and certification of newmaterials and the time it takes for designers tobecome familiar with them make it unlikelythat new materials or processes not now be-ing actively developed will be in commercialuse before the last half of the 1990s.

Several cobalt-free or low-cobalt alternativematerials have been investigated under NASAsponsorship (Conservation of Strategic Aero-space Materials Program, established in 1981,and pre-COSAM research activities.) Thesesubstitutes could provide alternative composi-tions for six widely used superalloy. Table 7-7 shows currently used superalloys selected forsubstitution research. Preliminary laboratoryexperiments suggest that cobalt may not beneeded in the high-volume Udimet 700 type su-peralloy (18 percent cobalt) which is used inturbine discs and blades. One evaluation of theinitial COSAM research hypothesized that


Table 7-7.–Nickel-Base Superalloy Selected for Cobalt Substitution Research by NASA

Typical engine Cobalt contentAlloy application Form Remarks (% weight)

WASPALOY . . . Turbine disc Forged Highest use wrought alloy in current 13.5eng ines

UDIMET-700 . . . Turbine disc F o r g e d Similar alloys used in various forms and 18.5(LC) ASTROLOY Turbine disc as-hip-powder applications(RENE 77) . . . . . Turbine blades CastMAR-M247 . . . . Turbine blades and wheels Cast Conventially cast, DS and single crystal 10,0RENE 150 . . . . . Turbine blades DS-Cast Highly complex directionally cast alloy 12.0

SOURCE Adapted from Joseph R Stephens, A Status Review of NASA COSAM (Conservation of Strafegfc Aerospace Mafer)als) Program, NASA Techn{cal Memorandum 82852 (Springfield, VA National Techn!cal Information Service, May 1982)

while definite conclusions are premature, itmay be possible to cut by one-half or even elim-inate cobalt now used in some nickel-based su-peralloys with little or no effects on mechani-cal properties or environmental resistance. (Anestimated 2.15 million pounds of cobalt wascontained in nickel-based superalloy primaryproducts in 1980, according to the NMAB. Thiscomprised about one-eighth of total apparentcobalt consumption in that year. )24

The COSAM substitutes are still in the lab-oratory stage of development and are manyyears away from actual use in a jet engine. Intheory, the COSAM alternatives could bebrought on line more quickly than an entirelynew material, since only slight adjustments inmanufacturing processes may be needed toproduce the low-cobalt substitutes. However,to commercialize these alloys fully could stillrequire 6 to 7 years and $6 million to $9 mil-lion per application—a commitment that en-gine makers will find difficult to justify, givencurrent low-cobalt prices. Hence, their post-COSAM development may be delayed until aperceived need arises.

Over the next 10 to 15 years, strategic ma-terials conservation could also be a side benefitfrom several advanced superalloy productiontechniques that are approaching commercial-ization—simply because some of the experi-mental prototypes and research materials happento contain little or no cobalt. These processesmay not necessarily conserve strategic materi-

Z4Nationa] Materials Advisory Board, Cobalt ConservationThrough Technological Alternatives, National Research Coun-cil, Publication NMAB-406 [Washington, DC: National AcademyPress, 1983), pp. 24 and 47.

als over the long run, however, if it turns outthat cobalt provides a performance benefit overthe experimental prototypes.

One group of these new processing methodsis “rapid solidification, ” in which metals aresolidified so quickly that the resulting distri-bution of elements is nearly homogeneous, hav-ing few inclusions that could initiate fatiguecracks. Moreover, previously unattainable al-loy compositions with superior properties canbe obtained in some cases, Experimentalcobalt-free superalloy powders producedthrough various rapid solidification processeshave been shown in early experiments to havesome advantages over conventionally proc-essed alloys. Detailed information on rapidsolidification processes and their prospects assubstitutes for strategic materials is providedin the Advanced Materials section of this chapter.

The capability to produce directionally solidi-fied eutectic superalloy is another of the re-cent processing advances. Over the past twodecades considerable effort has been devotedto developing this technique. When superalloyare produced in this manner, they are strength-ened by the formation of microscopic carbideor intermetallic fiber reinforcements. Most ofthe experimental alloys have comparativelylow levels of chromium and cobalt—4 percentand 3 to 10 percent respectively. As with otheradvanced processes and materials, the key ob-jective of eutectics development is not to con-serve strategic materials, but to increase tem-perature capabilities of turbine blades andvanes. Eutectic superalloy could increase theallowable operating temperature of these com-ponents by about 100° F compared to currentlyavailable single-crystal alloys.


Although work on eutectic alloys is progress-ing, they have yet to receive qualification forengine use. Technical problems include inferi-or transverse properties and poor oxidationand corrosion resistance. Cost of these alloysis high because the processing times are high;a eutectic blade can be withdrawn from the fur-nace at only about one-fourth inch per hour,However, eutectic R&D has had active supportby engine producers (General Electric andUnited Technologies) as well as scientific sup-port at government laboratories and univer-sities.

The medium-term (1990-2000) prospects forreducing cobalt and chromium in jet enginesare difficult to assess because new materialswill be used as new jet engines are introducedinto military and civilian aircraft. The selec-tion of these materials will be performancedriven, and while some materials may containlittle or no cobalt, others almost certainly will.Development of the COSAM alternatives to thepoint of commercial use is possible over thisperiod, but these materials will serve as sub-stitutes for currently used superalloys which

will comprise a declining portion of superal-loy use. It is also possible that, over this period,a breakthrough in basic science will occurwhich will lead to a better understanding of theprecise role of cobalt in superalloy, with pos-sible reductions of cobalt in the design of newalloys. Improved understanding of the role ofcobalt and other strategic materials in super-alloy is a key purpose of the COSAM program.

Long-Term Prospects

Over the long term, several classes of newmaterials that are completely free of cobalt orchromium may come into use. These alterna-tives are being actively pursued because oftheir potential to extend the maximum oper-ating temperatures (and thus performance) ofturbine blades beyond the current limits ofaround 1,150° C or 2,100° F. These materialsinclude ceramics, composites, and monolithicintermetallic compounds (or long-range ordermaterials) and are discussed in detail in thenext section. Table 7-8 summarizes potentialapplications for these advanced materials inthe hot section of jet engines,

Table 7-8.—Use of Structural Materials Under Development to Reduce Cobalt andChromium Usage in Hot-Section Parts

Composition (percent weight)

Material c o Cr Suitable componentsRapid solidification processed superalloy . . Varies Varies Combustor liners; cases; turbine blades,

vanes, discs, seals.Long-range order (intermetallics):

Ni . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . — — HP turbine discs (combustor liners; HPturbine vanes, blades)

Ti — LP turbine discs, blades, vanes; cases,Fe j I 111 I 1 ; I j ~ 1 : 111 j 11 I ; 1 I I 11 I 111 I I ~ 111 ~ — Combustor liners; LP turbine discs, blades,

vanes; casesDirectionally solidified eutectics . . . . . . . . . . . 3-1o 4 Turbine blades, vanesOxide dispersion strengthened superalloys . . — 15-20 Turbine vanes; (combustor liners, turbine

blades).Fiber-reinforced (metal matrix composite)

superalloy . . . . . . . . . . . . . . . . . . . . . . . . . . . . — 15 (matrix) Turbine blades, vanes; combustor liners;cases

Monolithic ceramics . . . . . . . . . . . . . . . . . . . . . . — — Turbine discs, vanes, blades, seals; cases;combustor liners

Ceramic-ceramic composites . . . . . . . . . . . . . . — — Turbine vanes, blades, casesCarbon-carbon composites . . . . . . . . . . . . . . . . — — Combustor liners; cases; afterburners;

nozzles; turbine discs, vanes, bladesKEY” HP = High pressure

LP = Low pressure.( ) = Less likely application— = Minimal or none

SOURCE: Office of Technology Assessment.

——


Advanced

There is currently a great deal of interest inthe development of advanced materials suchas rapid solidification processed materials,long-range order intermetallics, ceramics, andcomposites. This interest is driven by the im-pressive array of properties these new materi-als offer. They not only offer enhanced prop-erties, but often entirely new combinations ofproperties, as well, A side benefit of advancedmaterials is their use of little or reducedamounts of strategic materials.

Many advanced materials are still undergo-ing R&D and have thus far seen limited com-mercialization, In selected component appli-cations, some advanced materials are nowbeing used. The number of applications for ad-vanced materials should increase appreciablyduring the next 5 to 20 years—especially wheremajor design modifications are not needed. Inmost critical applications where performancestandards tend to be exacting, however, theywill require much more R&D before they seewidespread use,

Although growth in the use of advanced ma-terials is expected, the overall effect of theiruse on future strategic material needs is un-clear. Some major technical problems (e.g., thebrittleness of ceramics, difficulties in repair-ing composites, etc.) must be solved before theycan be used in many critical applications.Moreover, advanced materials will not neces-sarily be used as direct replacements for ex-isting materials. In many applications, thesenew materials are so different from the alloysubstitutes described previously that redesignof entire systems is often necessary to benefitfully from their properties. In addition, use ofstrategic materials may just as easily increaseas decrease as these new materials are adopted.For example, using advanced materials in thehot section of a gas turbine engine to raise itsoperating temperature may increase the tem-perature in a cooler section of the engine to apoint where it requires the use of strategicmaterials. Yet, using advanced materials (e. g.,composites) to make an aircraft lighter may al-

Materials

low the use of smaller engines containing lessamounts of strategic materials. In an economicsense, advanced materials and materials con-taining strategic elements may be both substi-tutes and complements.

The various industries involved in develop-ing and producing advanced materials are do-ing so because of a belief in the promise of fu-ture economic benefit from the introduction ofthese materials in existing and entirely new ap-plications, not because they foresee a role forthem as materials substitutes. The advancedmaterials industry has the potential to make alarge contribution to future U.S. gross nationalproduct (GNP), The U.S. market for advancedceramic materials, for instance, has been pro-jected at $5.9 billion by the year 2000, anamount 10 times the 1980 market. 25

This emerging U.S. advanced materials in-dustry faces global competition, especiallyfrom Japan and Western Europe, in materialsdevelopment, processing, and commercializa-tion. Today, some processed ceramic materialsand components of composites are only avail-able from foreign sources. In some instances,the United States is credited with the basic re-search on some material components for whichJapan now holds most of the processing capac-ity. In others, process licensing has been madeavailable to U.S. firms for foreign patentedmaterials.

Compared to their metallic counterparts, ad-vanced materials have relatively brief historiesof use, and this absence of a proven track rec-ord often makes designers and their industriesreluctant to use them. Different societies ap-proach institutional barriers to commerciali-zation in different ways. In the United States,the standard engineering education still pro-vides little, if any, formal training in the useof advanced materials, Industry must bear thecost of continuing education. In Japan, indus-

Z5U .S. Department of Commerce, A Competiti\re Assessmentof the U.S. Advanced Ceramics Industry [Washington, DC: U.S.Government Printing Office, March 1984), p. xiii.


tries are willing to introduce advanced mate-rials to the marketplace at a lower level of con-fidence in their eventual success than in theUnited States. The risk of failure is reduced bytesting new materials in everyday items suchas scissors or high-value glamour products,such as sporting goods.

The following sections present the currentstate of the art of these advanced materials,and, where known, potential areas for strate-gic material savings. It must be kept in mind,however, that many unknowns exist, and therapid advance of the science of these materialscould change their prospects in only a shorttime.

Ceramics

Advanced ceramic materials are an emerg-ing technology with a very broad base of cur-rent and potential applications and an ever-growing list of material compositions (see table7-9). While this dynamic situation makes it dif-ficult to quantify their future impact, it doesnot appear that advanced ceramics will replaceany substantial portion of the U.S. demand forfirst-tier strategic materials within the next dec-ade. Beyond 2010, a larger potential for sub-stitution exists if ceramic rotating parts are suc-cessfully applied in gas turbine engines. Inorder for this major materials substitution tobe technically feasible, however, the brittlenesstendency of ceramic materials must be over-come by improvements in material propertiesand processing technologies and the use of cer-amics must be integrated with system designsthat reduce the ways in which stresses areloaded on ceramic parts.

Most ceramic raw materials (see table 7-10)are not considered potential strategic materialsbecause they are available in large quantitiesfrom domestic sources. However, the UnitedStates is competing with other countries in ad-vanced ceramics R&D, and loss of a leadershiprole in the development and use of ceramicmaterials could ultimately result in a depen-dence on international sources (primarily Ja-pan) for processed ceramic materials andproducts.

While a potential decrease in U.S. consump-tion of strategic materials is an important ben-efit of ceramic use, the promise of performanceimprovements is the main force driving the de-velopment of advanced ceramic materials. Thesought-after properties of advanced ceramicsinclude wear resistance, hardness, stiffness,corrosion resistance, and relatively low density(providing a weight savings that can translateinto energy savings), A major attraction, how-ever, is a high melting point and accompany-ing mechanical strength at high temperatures.Ceramics offer one of the best possibilities forraising the operating temperature of heat en-gines and power generating equipment; and asthe operating temperature in these systems isincreased, system efficiency in energy conver-sion can increase, resulting in cost savings. Themetallic superalloy currently used in jet engines limit operating temperatures to about2,000° F, whereas ceramic materials can with-stand temperatures up to about 2,500° F. Com-plicated and energy-consuming cooling sys-tems now must be used—even in relativelylow-temperature engines such as automobiles—to maintain the integrity of metals at operat-ing temperatures. Ceramic materials can alsobe used to increase the energy efficiency ofmany high-temperature processing systems.The excellent wear-resistance properties of cer-amics could increase productivity in themachining, chemical, and metal processing in-dustries, where wear and corrosion resistanceare critical. Box 7-A provides detailed informa-tion on the properties of ceramics and on theprocesses for making them.

Although research into some areas of ad-vanced ceramics is still in the developmentstages, new roles in electronics and wear-re-sistance applications are being filled by ceram-ics. Neither the economic viability nor the tech-nical capability of using ceramics in many ofthe structural applications (e.g., heat engines)has yet been demonstrated. Although the basicceramic raw materials (e. g., silicon, alumina,magnesium) are plentiful and inexpensive, theprocedures necessary for converting the rawmaterial into a usable form (usually an ultra-fine powder) and then a final product can beexpensive. It has been estimated that from 25


Table 7-9.—Current and Prospective Uses for Advanced Ceramics

First-tier strategicmaterials substitution

Ceramic material Current and potential applications opportunities-. . .Electric:Insulating (AI2O3, BeO,

MgO)Low-firing and/or glass cer-

amics, ferroelectrics(BaTiO 3, SrTiO3)

Piezoelectric (PZT)

Semiconductor (BaTiO3

SiC, AnO-Bi2O3, V2O5,and other transitionmetal oxides)

Magnetic:Soft ferrite

Hard ferrite

Optical:Translucent aluminaTranslucent magnesium

oxides, muIIite, etc,Translucent Y2O3-ThO 2

ceramicsPLZT ceramics

Chemical:Gas sensor (ZnO, Fe2O3,

SnO2)Humidity sensor

(MgCr 2O4-TiO2)Catalyst carrier (cordierite)Organic catalyst

Electrodes (titanates, sul-fides, borides)

Thermal:ZrO2-basedAl2O3-basedSi-based

IC circuit substrate, package, wiring substrate, resistor sub-strate, electronics interconnection substrate,

Ceramic capacitor.

Vibrator, oscillator, filter, transducer, ultrasonic humidifier,piezoelectric spark generator.

NTC thermistor:temperature sensor, temperature compensation,

PTC termistor:heater element, switch, temperature compensation.

CTR thermistor:heat sensor element.

Thick film thermistor:infrared sensor.

Varistor:noise elimination, surge current absorber, lighting ar-restor.

Sintered CdS material:solar cell.

SiC heater:electric furnace heater, miniature heater.

Solid electrolyte for sodium battery.ZrO2 ceramics:

oxygen sensor, pH meter fuel cells.

Magnetic recording head, temperature sensor.

Ferrite magnet, fractional horsepower motor, powderstapes and discs (u-FezOS, CrO2).

High-pressure sodium vapor lamp.

—

Low-temperature firing per-mits use of copper in-stead of tungsten, molyor PGM wires, nickel in-stead of PGM elec-trodes.

—

—

Pt, Pt-Rh heaters, Ni-chrome heaters

Ceramics for Co-Sinmagnets

forCeramics for AINiCo

magnets

For a Iighting tube, special-purpose lamp, infrared transmis-sion window materials,

Laser material.

Light memory element, video display and storage system,light modulation element light shutter, light value.

Gas leakage alarm, automatic ventilation fan; hydrocarbon,fluorocarbon detectors.

Cooking control element in microwave oven.

Catalyst carrier for emission control.Enzyme carrier, zeolites, other ceramics.

Electrowinning aluminum, photochemical processes, chlo-rine production.

Infrared radiator, thermal barrier coatings.

——

—

Reduced use of Pt-groupcatalyst

—

—Catalytic processes may

replace Co, Pt—

Reduced use of W, Cr, Co,Ni


Table 7-9.—Current and Prospective Uses for Advanced Ceramics—Continued

First-tier strategicmaterials substitution

Ceramic material Current and potential applications opportunities

Mechanical:Cutting tools Ceramic tool, sintered SBN. WC-Co cemented cutting(AI2O3, TiC, TiN, others) Cermet tool, artificial diamond. tools and high-speed

Nitride tool. steels (Cr)Wear resistant (AI2O3, ZrO2) Mechanical seal, ceramic liner, bearings, thread guide, pres- Hard facing alloys

sure sensors. (Cr, Co, Mn)Heat resistant (SiC, AI2O3, Ceramic engine, turbine blade, heat exchangers, welding Superalloy (Co, Cr)

Si3N 4, ZrO2, others) burner nozzle, high-frequency combustion crucibles.

Biological:Alumina ceramics implan- Artificial tooth root, bone, and joint. Bone and tooth implants

tation (Pt, Co, Cr-basedHydroxyapatite bioglassSOURCE’ Elaine P. Rothman, George B KenneY, and H. Kent Bowen, MIT Materials Processing Center, Poterrtlal of Cefarrric Materla/s to Replace Gobal(, Chromium,

Manganese, and Platinum in Critical Applications, OTA contract study, January 1984.

Table 7.10.—Some Advanced Ceramics Material Families

Families Chemical formula Elements

Alumina . . . . . . . . . . . . . . . . . . . AI2O3 Aluminum, oxygenAluminum silicate. . . . . . . . . . . AISi Aluminum, siliconBarium titanate . . . . . . . . . . . . . BaTiO 3 Barium, titanium, oxygenLAS . . . . . . . . . . . . . . . . . . . . . . . Lithium, aluminum, siliconMagnesium silicate . . . . . . . . . MgSi Magnesium, siliconMAS (cordierite) . . . . . . . . . . . . 2MgO~5Si0,02Alz0, Magnesium, silicon, oxygen,

aluminumMagnesia . . . . . . . . . . . . . . . . . . MgO Magnesium, oxygenSilicon carbide . . . . . . . . . . . . . SiC Silicon, carbonSilicon nitride . . . . . . . . . . . . . . Si3N 4 Silicon, nitrogenSiAION . . . . . . . . . . . . . . . . . . . .(various alloys of silicon nitride and alumina)Zirconia . . . . . . . . . . . . . . . . . . . ZrO2 Zirconium, oxygen

PZT (partially stabilized zirconia) Zirconia with particles of calcia,magnesia or yttria

SOURCE: Office of Technology Assessment.

to 75 percent of the production cost of ceramiccomponents is due to a high rejection ratecaused by the poor reproducibility of currentprocessing steps.26 As new manufacturing tech-nologies mature and the ability to design withbrittle materials increases, prices are projectedto become competitive with existing metallictechnologies. As yet, however, mass produc-tion of many advanced ceramics does not yetoccur. Scaling up an experimental process toa commercial manufacturing level of produc-tion, while retaining the desired properties of

ZaE]aine p, Rothman, George B. Kenney, and H. Kent Bowen,Materials Processing Center, Massachusetts Institute of Tech-nology, Potential of Ceramic Materials to Replace Cobalt, Chro-mium, Manganese, and Platinum in Critical Applications, OTAcontract report, January 1984, p. 240.

the materials and obtaining production relia-bility, has not often been achieved.

Ceramics as a Strategic Material Substitute

A growing market for advanced ceramics ex-ists in a number of applications, with limitedimplications for the use of strategic materials,Strategic material substitution, however, mayhave a higher potential in the long term (2010and beyond), particularly in the eventual useof advanced ceramics in aircraft gas turbineengines and, to a lesser extent, as componentsin automotive gas turbine and heavy vehiclediesel engines.

As shown in table 7-11, ceramic materials aredisplacing some first-tier strategic materials in

.— ——


Box 7-A.—Ceramics Primer

Ceramics, derived from the Greek word“keramos,” meaning “burnt stuff,” is a gen-eral term for inorganic,27 nonmetallic materi-als processed or consolidated at high temper-atures. Traditionally, ceramics has referred tothe family of earthenware, brick, glass, por-celain, and enamels in common use. The fieldnow encompasses a wide range of materialsand applications.

Traditional types of ceramics are made fromnatural raw materials such as clay, silica, andfeldspar and produced using relatively simplechemical processing, forming, and firing steps.Advanced ceramic products, on the otherhand, are produced from ultrafine powderforms of synthetic materials derived from thenatural raw minerals. The powder productionphase of advanced ceramics processing hasbecome increasingly critical. Purity, particlesize, shape, and distribution of particles andhow they agglomerate must be rigidly con-trolled in order to produce reliable, reproduc-ible components, To attain such high-quality,new techniques such as sol-gel, coprecipita-tion, and laser synthesis have been added toconventional powder production and agglom-eration methods.

Because a great number of materials areclassified as ceramics, a wide range of prop-erties are available; and ceramic materialshave many characteristics that distinguishthem from metals. They are generally morestable chemically and thermally and are bet-ter insulators than metals. On the other hand,they are much stronger in compression thanin tension and do not have the same ductil-ity, or “forgiving” nature, of metal. Ceramicsare harder and more rigid than either metalsor plastics and are more stable (retain theirlow-temperature properties) at high temper-atures.

Owing to their lack of ductility, ceramicproducts cannot be formed by the stampingor forging processes used for metals. Instead,they are generally processed directly fromhighly refined raw material by the consolida-tion of powder. (Melt formation is used to

form glass and single crystal ceramics.) Thepowder is first formed to the desired shape.Forming methods include isostatic pressing,injection molding, and slip casting. This“green body” preform is then further densi-fied by the application of heat (sintering) orthe simultaneous application of heat and pres-sure (two such processes are hot-pressing andhot-isostatic pressing). Reaction bonding andreaction sintering are special sintering proc-esses during which the final composition ofthe ceramic material is obtained along withdensification. The combination of processesselected to produce a ceramic material will af-fect its ultimate properties.

Ceramics are brittle and fracture with littleor no warning. This characteristic has beenthe material’s major barrier to expansion intoa wide range of applications, both technicallyand institutionally. Ceramics must be consid-ered and used in ways different from thosetaught traditionally to designers and engi-neers schooled in the use of metals. Becausemetals bend and deform prior to reaching apoint of fracture, ceramics cannot usually bedirectly substituted for metal alloys on a one-for-one basis. Instead, redesign of componentsand systems to eliminate or minimize load-bearing (stresses) are often necessary in orderto substitute a ceramic material.

A considerable amount of the research inceramics centers around how to reduce, copewith, or design around this brittleness. Re-search takes three approaches: 1) basic re-search to increase the knowledge base and un-derstanding of the behavior of the materials,2) improvement of processing technologies toreduce the probability of brittle failure, and3) investigation of how varying material com-positions can affect ceramic properties.

Brittle failure results from microscopicflaws (cracks), solid inclusions, and voids inthe microstructure28 of finished products in-evitably introduced to a ceramic material dur-ing processing. The likelihood of brittle fail-ure increases with the size of such flaws, andtension loading on a part will lead to the

ITSubstances that do not contain carbon except as a minor con-stituent.

ZaThe detailed arrangement (size, nature, and distribution) ofphases (combinations of elements) that constitute the overall ma-terial.


growth of existing flaws (crack propagation).New processing techniques aim at reducingflaw size and population by the use of homo-geneous powders and forming procedures.Greater processing reproducibility is anothergoal.

Another, complementary method of de-creasing the probability of fracture of cer-amics is to increase the energy required to ex-tend a crack in the material. Such a barrierto crack propagation is provided by introduc-ing toughening mechanisms into the powdersbefore processing. Examples include zirco-nium oxide particles embedded in aluminumoxide and calcia, magnesia, or yttria added tozirconia to create partially stabilized zirconia(PSZ).

wear-resistant applications such as cutting tooltips, pump seals, bearings and nozzles, and inheat-resistant applications such as heat ex-changers. Turbochargers with ceramic rotorsmay be offered by one Japanese automobilemanufacturer within the next few years.

Wear-resistant parts today are often madefrom cemented tungsten carbide materials inwhich cobalt is used as a binder. This mate-rial accounts for 9 percent of the annual U.S.consumption of cobalt, more than half of whichis estimated to be used in these wear-resistantapplications. (Another major end use is ma-chine dies.) In heat-resistant applications, ce-ramic materials such as silicon carbide, siliconnitride, and aluminum silicates can replacestainless steels and other heat-resistant alloyscontaining chromium, cobalt, and some man-ganese. While it is difficult to quantify the in-dividual quantities of these metals used inwear- and heat-resistant applications, the over-all amounts are thought to be small. The sub-stitution of ceramic materials will, therefore,result in minor strategic material savings. Ad-ditional indirect savings may be generated byhigher temperature operations, energy savings,and weight reductions made possible by theuse of ceramics.

The ability to identify the flaws cm increasethe reliability of ceramic products. Nonde-structive evaluation (NDE) techniques are be-ing developed (by both industry and the Fed-eral Government) to determine flaw size,shape, concentration, and type with an aimtoward predicting when component failurewill occur. As yet, there is no “perfect”method for detecting all types of flaws in ce-ramics. Many methods are not applicable tothe production line or are simply too costlyand time-consuming, NDE techniques includeultrasonic, radiography, optical, and thermo-graphic methods.

If successfully introduced in the rotor sec-tion of turbochargers, advanced ceramics willfind their first commercial rotating, structuraluse and will replace nickel superalloys andnickel-iron alloys containing cobalt and chro-mium, respectively. With 100 percent penetra-tion in the automotive market, ceramic mate-rials would replace less than 1 percent ofcurrent U.S. cobalt and chromium annual con-sumption, but may inhibit a growing use ofstrategic materials.

Current automotive engines consume a neg-ligible amount of first-tier strategic materials,but operating engine conditions require air pol-lution control devices that consume 1.5 percentof the chromium and 34 percent of the PGMsconsumed annually in the United States. It hasbeen suggested that the use of ceramic gas tur-bine and diesel automobile engine technologiesmay alter these pollutants, thereby changingthe material requirements for catalytic con-verters. In aircraft gas turbine engines, on theother hand, a direct material substitution couldoccur with the replacement of superalloycontaining cobalt and chromium currently con-sumed in portions of such engines. (The avia-tion industry annually consumes approxi-mately 40 percent of the U.S. cobalt demand

Table 7-11. —Potential of Advanced Ceramics to Substitute for First-Tier Strategic Materials

Current strategic Ceramic materialsmaterial use currently used Extent occurrent

estimated percent of or under Advantage to usePrimary factors affecting adoption commercialization—

Application annual U.S. consumption consideration of ceramics Technical Economic lnstitutional U S and world—

Near term (before 1995):Wear resistance.

Cutting tool tips Cobalt, as binder mtungsten carbide5 percent

Seals, bearings, Cobalt, as binder mnozzles, etc tungsten carbide

3 percent

Alumina, silicon Increased productivitynitride, sialon

Overcoming Inadequatefracture toughness

Appears competitive withtungsten carbide

Most U S machine tools cannot

accept ceramic bits Lack ofinformation within machine toolindustry

Need to standardize parts Con-sumer awareness and lack ofdesire to change; pumps are areplacement parts market,longer seal life is not seen asan advantage to producers

Change over to electrical induc-tion heating which does notuse recuperators. Depressedstate of the domestic steelindustry and metal processingindustries has inhibited change

Ceramics will be used if theydemonstrate superiorperformance

2% of U.S. marketHigher in Japan andWest Germany

Alumina- Improved wear and cor-zirconia, rosion resistancesilicon carbide

No significant barriers Competitive withtungsten carbide ex-cept large (>8 inchdiameter seals)

20% of U.S. and worldmarket

Improved joiningtechnology (ceramic/ceramic. ceramic/metal) andreproducibility of SICtubes in processing

Overcoming difficulties inceramic/metal joining;improving reproducibil-ity of the ceramicrotors

Higher initial capital in-vestment than metallicheat exchangers Highcost of SiC tubing

< 5% of U.S. marketPossibly higher in Japan

Heat exchangers Small amounts ofLarge Industrial chromium in high-Small single burner temperature stainless

recuperators steels

Silicon carbide Energy savings Longerfurnace life

Cordierite

Turbochargers Superalloy containing(automotive) Chromium. (0.02 percent)

Cobalt: (0.4 percent)

Silicon carbide, Higher temperaturesilicon nitride capability with lower

mass Potential fortower costs

Current cost of produc-ing the ceramic rotorIS high, but economiesof scale are predicted

Expected limited in-troduction byJapanese soon, possi-ble market penetrationby 1990

Long term (after 1995):Automotive diesel

engine (cylinder,pistons, sensors)

Some chromium andcobalt in heat resistantand specialty steels;in addition, chromium:1 5 percent, PGMs 34percent in automobilecatalytic converters(Use of ceramic partswill alter operatingtemperatures of en-gines, causing possi-ble change inconverter material re-quirements )

(same as above)

Silicon, silicon Higher engine efficien-carbide, silicon cies potential. Light-nitride, zirconia weight engine

components

Improved fracture tough-ness, reproducibilityand reliability of parts

Only prototype parts arecurrently produced,generally, hot pressedprototype parts requirediamond machiningwhich IS an expensivemass production tech-nique. New processingtechniques couldgenerate significanteconomies of scale

Almost revolutionary change inengine style IS required to fullyrealize ceramics potential

Only several demonstra-tion engines so far

Automotive gas turbinecombustors, shrouds,and rotors

Silicon carbide, Higher engine efflclen-silicon nitride, cies, ability to burnsialon, lithium, any fuel, lower massaluminum Potentially lower costsilicate

improved fracture tough-ness, thermal shockresistance, reproduci-bility and reliability

High cost of processingdue to current tech-niques and Iimitedproduction volumes

r ‘Proof of concept” enginesfollow-on design will needthorough, exhaustive road test-ing to overcame brittle imageof ceramics

Only prototypes anddemonstration testing

NOTE These apphcahons are not meant 10 be all Incluswe but represent key potential applications

SOURCE Elaine P Rothman, George B Kenney, and H Kent Bowen MIT Materials Processing Center Poferrt@ of Ceramic L4aterlak 10 Replace CobaH C/Irornwn Manganese and Plaflflum In Wlca/ App/IcatIorM OTA contract study, January 1984


and less than half a percent of its chromiumdemand, and most of this material is used inthe manufacture of jet engines.)

Owing to their higher temperature capabil-ities, resistance to corrosive environments, lowinertial mass, potentially low cost, and theready availability of raw materials, ceramicscould become an integral part of future powergenerating technologies. In contrast to currentand near-term applications, however, majortechnical barriers must be overcome before ce-ramic components for diesel and gas turbineengines can advance from demonstration proj-ects to commercialization. Improvements areneeded in material properties (most signifi-cantly, fracture toughness), processing andfabrication techniques, ceramic-ceramic andceramic-metal joining capabilities, testing pro-cedures, and design methodologies. Ceramiccomponents must be reliably produced andmanufacturing processes must be capable ofa high degree of reproducibility, neither ofwhich is possible at the current state of thetechnology.

The Ceramics Market and Industry

The worldwide market for advanced ceram-ics in 1980 was estimated to be $4.25 billion. 29

Electronic components represent the primarymarket for ceramics, with cutting tools andwear parts second and third, respectively.Roughly half of the present overall demand isbeing met by Japanese companies, whose salesexceeded $2 billion in 1980.30 While the elec-tronic segment now accounts for more thantwo-thirds of the total market and offers sig-nificant growth potential, it may eventually bedwarfed by the ultimate size of the high-tem-perature applications market.

Indicative of a high level of uncertainty, pro-jections made to estimate the value of the ad-

vanced ceramics market by 2000 vary widely.An American Ceramics Society study31 pro-jected a $20 billion world market, half of whichwould be domestic. The U.S. Department ofCommerce was more conservative in a studyreleased in 1984. It projected total domesticshipments (as equivalent to future market po-tential) of advanced ceramics of $5.9 billion.Included were electronics shipments of $3.5billion; heat engines, $840 million; cuttingtools, $960 million; and wear parts, $540 mil-lion.32 In yet another estimate, advanced ce-ramic usage in automotive engines alone wasprojected to reach $30 billion on a worldwidebasis by the year 2000.33

Except in electronics, advanced ceramicmaterials have penetrated a very small shareof their recognized end use markets world-wide, primarily due to the state of the technol-ogy and relatively high costs of its products.While low-volume production adds to thesehigh costs, demonstrated technical perform-ance will not necessarily create markets for ad-vanced ceramics. Roughly half of the cost ofa typical ceramic component is estimated tobe due to production rejects.34 An incrementalintroduction into most markets is expected un-til ceramic component mass production tech-niques are developed which can reproduciblyfabricate reliable products and customer ac-ceptance can be firmly established. In auto-mobile markets, revolutionary ceramic enginedesigns may have to await a lengthy provingprocess prior to successful commercialization.If it is successful, the ceramic turbocharger—the first commercial structural heat engine useof advanced ceramics—can provide invaluableinformation for this process and the beginningsof institutional acceptance of the structural ca-pabilities of advanced ceramics.

The essence of the advanced ceramics busi-ness is that common starting materials are con-

~9ROthrnan, et al,, op. cit., p. 238.~Ibid., Japanese firms were estimated to hold 52 percent of

the worldwide ceramic powders market; 61 percent of electronicIC packages/substrates; 91 percent, piezoelectrics; 43 percent,capacitors; 63 percent, thermistor/varistors; 79 percent, ferrites;II percent, gasdlmmidity sensors; 44 percent, translucent ceram-ics; 12 percent, cutting tools (carbide, cermet); and 48 percent,structural ceramics (heat and wear resistant).

Slrbido

32u.s. Department of Commerce,, op. cit., p. 13. The Depart-ment of Commerce cautioned in its study that it is too early inthe history of this new industry to predict its future with a highlevel of confidence.

33AccOr&ng to Kent Bowen of MIT, as quoted in Rothman,et al., op. cit.

s41bid.


verted into high value-added commodities andcomponents by sophisticated, high-technologyprocessing and manufacturing systems. Exact-ing standards require extensive quality control.Generally, material producers in the ceramicsindustry have been and still remain verticallyintegrated; thus, raw materials are processedand fabricated into component parts within asingle company. Relatively few producers sup-ply ceramic raw materials, and even fewer sup-ply new advanced ceramic powders. The evolv-ing advanced ceramics industry consists oftraditional ceramics firms expanding into newapplications, new end users taking on the taskof being materials suppliers, and conventionalmaterials firms expanding into the ceramicsarena.35

The United States is not alone in its interestin advanced ceramic materials. It already iscompeting with and will continue to encoun-ter stiff competition from Japan and WesternEurope in tapping future markets. The Japa-nese industry is currently the sole source forsome high-grade ceramic powders (e. g., siliconcarbide) and has eclipsed the rest of the worldin supplying the electronics market. se A Brit-ish firm, which holds numerous patents forsialons (a ceramic composed of oxides and ni-trides of silicon and aluminum), now licensesothers to manufacture these materials.

Japan began its comprehensive advancedceramics R&D program only in 1977, but itsgovernment-industry-university collaborativeeffort is widely regarded as the best organizedand financed in the world, The Japanese are,of course, more materials and energy import-dependent than the United States; and a primegoal of their research efforts is to ease that de-pendence. But they also view advanced cer-amics as a technology which will be part of an

tsFOr a review of the status of the U.S. advanced ceramics in-dustry and the firms involved, see the U.S. Department ofCommerce, A Competititre Assessment of the U.S. AdvancedCeramics Industry, op. cit.

t@Not a]] such sales in the United States are imports, however.Kyocera International, a subsidiary of Kyoto Ceramic Co. of Ja-pan, established production facilities in San Diego in 1971 whichnow supply 70 percent of the U.S. demand for ceramic packag-ing for integrated circuits. See “The Japanese Score on a U.S.Fumble, ” Fortune magazine, June 1, 1981, pp. 68-72,

industrial base for the future. In an issue of TheJapan Industrial & Technological Bulletin37 i n1983, R&D in ceramics is recognized as involv-ing “huge investment risks” and requiring “arelatively long lead time before the commer-cialization of these materials. ” As such, thestudy concluded that the Japanese government“should take the main role in promoting ad-vanced and fundamental research as well asdevelopment. ” And, the primary objectives ofthe Fine Ceramics Office set up in July 1982under the auspices of the Ministry of Interna-tional Trade and Industry (MITI) are to “geta comprehensive picture of the domestic fineceramics industry, systematize the industry,consolidate the industry’s foundation andadopt comprehensive policies designed to pro-mote the industry’s sound growth. ”

While the United States, Japan and WesternEurope have all followed interdisciplinary ap-proaches in their independent research efforts,the U.S. effort has leaned toward basic re-search and design methodologies while othershave emphasized materials supply and proc-essing. As a consequence, some feel that theUnited States may end up lagging behind inthe implementation and exploitation phases ofadvanced ceramics technology. In advancedceramics (as in other new technologies), theJapanese seem willing to take the risk to applystate-of-the-art materials to consumer products.This provides field testing for improvement ofthe knowledge base of the technologytion experience and cost reductionscome to finance further research effortswhile gaining customer acceptancematerials,

produc-and in-

, all thefor new

If one assumes that the Japanese rather thanthe United States becomes the dominate fac-tor in an all-important future automobile ce-ramic engine market, the United States couldbe adversely affected by a decline in the GNP,loss of employment opportunities, shift in the——

37 Japan Externa] Trade Organization, The Japan Industrial ~Technological Bulletin: The Development of Structural Fine Cer-amics in Japan, Specia] Issue, No. 15. 1983, pp. 6-7. Note thatJapan uses the term “fine ceramics” for what is commonly re-ferred to as “advanced ceramics” in the United States.


balance of trade, and loss of savings in energycosts .38

One aspect of the expanding ceramics indus-try for which there is little data is the possibleenvironmental, health, and safety effects on thecommunities and workers where the process-ing occurs. While some may assume that theseprocesses may be “cleaner” than those of ex-isting metal production, the statistics as theyare now collected and aggregated by the Envi-ronmental Protection Agency and the Occupa-tional Safety and Health Administration basedon the traditional ceramics industry do not cor-respond to the future industry,

Research in Ceramics Applications

Ceramics is an ancient art. Despite—or be-cause of—the age old and common use of ce-ramics, it remained essentially an art until re-cently, when more exacting standards wereasked of the materials. One major engineeringtextbook on ceramics states in its 1976 editionthat:

. . . until a decade or so ago, ceramics was inlarge part an empirical art, Users of ceramicsprocured their materials from one supplier andone particular plant of a supplier in order tomaintain uniformity. Ceramics producers werereluctant to change any detail of their process-ing and manufacturing (some still are), The rea-son was that the complex systems being usedwere not sufficiently well known to allow theeffects of changes to be predicted or under-stood, and to a considerable extent this re-mains true.39

British scientists conducted much of theoriginal research in the 1950s and 1960s in cer-amics theory, raw materials development, andprocessing methods. Not until the 1970s wereceramics developed to the point where theycould be considered engineering materials inthat their chemical and physical propertiescould be altered to match intended functions

3LIL. R, Johnson, A, P. S. Teotia, and L. G. Hill, A Structura]Ceramic Research Program: A Preliminary Economic Analysis.ANL/CNSV-38. Argonne National Laboratory, March 1983.

wwr, D. Kingery, H. K, Bowen, and D. R. Uhlmann, ~ntroduc-tion to Ceramics, Zd ed, (New York: John Wiley & Sons, 1976),p. 1.

in various applications. This short period of de-velopment time probably contributes to therelatively low rate of usage of advanced ce-ramic materials so far,

Following is a discussion of the currentstatus of the research and use of advanced cer-amics in cutting tool, wear resistance, heat ex-changer, and heat engine applications.

CUTTING TOOLS40

Cutting tool applications represent a limitedbut growing and potentially valuable marketfor ceramic materials. At present the total U.S.market for cutting tools has been estimated at$2.2 billion per year. Advanced ceramic cut-ting tools hold 2 to 3 percent of this market(compared to tungsten carbide at 45 percent).41

Nine percent of the annual U.S. consumptionof cobalt is used as a binder in tungsten car-bide material.42

New cutting tools are continually beingsought to increase manufacturing productivityby attaining higher cutting speeds and reduc-ing the downtime of cutting machinery throughimproved lifetime of tool inserts. Ceramicmaterials have proven feasible in this applica-tion and may offer higher performance thanexisting cutting tool materials; but they mustcompete with new metal alloys, coatings, andprocessing methods (e.g., powder metallurgy)for market penetration. No one material meetsall cutting requirements in all applications, andadvanced ceramic cutting tools tend to behigher in cost than conventional tools,43 owingto their smaller volume production and morecomplex processing. This higher initial cost,however, can be mitigated by the higher cut-

— —.————aCutting tools are insert pieces—the cutting edge—held and

guided by machine tools. The process of machine tooling shapesand removes excess materials from manufactured products toproduce desired tolerances.

AIU.S. Department of Commerce, Op. Cit., P. 35.AZRothman, et a]., op. Cit., p. 168.‘sAccording to an interim draft report (January 1984) by

Charles River Associates for the National Bureau of Standards,Technological and Economic Assessment of Advanced CeramicMaterials: A Case Study of Ceramic Cutting Tools, a typical sili-con nitride cutting tool is currently sold in the $18 to $20 range,whereas typical tungsten carbide cutting tools are priced at $4to $5.

Ch. 7 —Substitution Alternatives for Strategic Materials ● 295

ting speeds, if downtime due to lower reliabil-ity is not excessive,

An increase in the use of advanced ceramicsis dependent on improvements in ceramic ma-terials and the machine tools in which they areused. Advanced ceramic materials have greaterabrasion, wear, and creep resistance than theircarbide counterparts, but less strength, fracturetoughness, and thermal shock resistance. Theattributes of ceramic materials provide su-perior performance at high cutting speeds(especially demanded by the automotive andaerospace industries), which can translate intoproductivity gains. But widespread conversionto advanced ceramic cutting tools will requireinvestments in new machine tools as many ofthose still in use have neither the speed, power,nor rigidity needed to use ceramic cutting toolseffectively.

While approximately two-thirds of currentceramic tool sales are alumina (Al2O3), intro-duced in the 1960s, the newest cutting tools inuse today are based on the silicon family. (Sili-con nitride exhibits twice the fracture tough-ness of alumina.) Rapid development of siliconnitride ceramics has been the result of acceler-ated research activity over the past decade onhigh-temperature structural ceramics for usein advanced energy conversion systems. FordMotor Co., for instance, is now moving towardcommercialization of its “S-8” material, whichwas developed during research on materials forgas turbine rotors.

Most of the direct research in cutting toolsin the United States is conducted by private in-dustry and has been estimated at $1 million peryear. 44 Indirect benefits may accrue, however,from the much heavier investments by govern-ment, industry, and academia in structural cer-amics R&D.

Japan and Western Europe are considered tobe ahead of the United States in the develop-ment and utilization of ceramic cutting tools.(About half of the advanced ceramic tools soldin the United States are imported from Japan.)The difference in higher usage has been attrib-

~41bid., p. 45.

uted to the fact that in the United States’ oldermachine tool industry equipment is outdatedand must be modernized or replaced before ce-ramic tools can be used to their full advan-t a g e .4 5

WEAR APPLICATIONSWear applications are often in low-tempera-

ture environments in which resistance to abra-sion and corrosion are the primary perform-ance goals. Applications include ball and rollerbearings, valves and pipefitting, industrialfasteners, and pumping equipment such asseals, liners, and nozzles. The traditionalmaterials for those applications are cementedtungsten carbide and wear-resistant steels (inwhich chromium is used as an alloying agentfor its hardenability). Up to about 3 percent ofU.S. cobalt consumption may be used in allwear-resistant applications and about 2 percentof chromium. Thus, strategic materials savingscould result from more extensive substitutionof ceramic materials in wear applications.

While the technical feasibility of wear partsmade from ceramics (primarily aluminum ox-ides, and silicon carbides, silicon nitrides) hasbeen demonstrated, the Department of Com-merce has estimated that ceramics currentlyhold less than 1 percent of the annual $3.3 bil-lion U.S. market.46 The extent to which theywill assume a greater share of these marketswill be strongly affected by performance versuscost tradeoffs. The current state of processingand fabrication techniques for ceramic wearparts (rather than raw materials costs) leads tothe higher initial costs than those for metalparts, Ceramics can, however, provide longerservice life than metals.

The potential to resist fatigue, corrosion, hightemperatures, and loss of lubrication betterthan metals make ceramic materials attractivefor ball and roller bearing uses, Their high costof fabrication, however, makes them imprac-

4sE Dow Whitney, “Process in Ceramics Research for Cut-ting Tools in the U. S., West Germany, Japan and Sweden, ” pa-per given at the National Science Foundation conference on Sub-stituting Non-Metallic Materials for Vulnerable Minerals, June1983, p. 1.

SeDepartment of Commerce, Op. cit., p. 35.


tical in many applications. Ceramic bearingstend to be consumed primarily by petroleumand chemical industries, which have demand-ing performance standards (e. g., in corrosiveenvironments) and in specialized aerospace ap-plications, all of which can absorb the high ini-tial cost.47 Pump seals are the largest wear ap-plication market now held by ceramics. Theproperties required are hardness, low friction,high resistance to corrosion, and high-tempera-ture capability. Ceramics (especially, siliconcarbide and silicon nitride) have been shownto be superior to metals in performance in thisapplication and, with improved manufactur-ing techniques and reduced costs, are expectedto assume more of the market. Nozzle partsmust withstand high wear and abrasion resis-tance properties which the hardness of ceram-ics provides. 48

Research in wear applications for ceramicsis primarily conducted by the private sector,much of which remains proprietary, resultingin little transfer of technology. The researchis concentrated on improving the properties ofthe materials, on manufacturing techniques toreduce costs, and on nondestructive evaluationmethods to gain reliability.

HEAT EXCHANGERS

Competitive pressure in high-temperature in-dustrial processes, as well as the rising cost ofenergy and the reduced availability of high-grade fuels in the 1970s, have led to the devel-opment and expanded use of energy conser-vation devices such as heat exchangers.49 Asin other high-temperature applications, the useof advanced ceramic materials in heat ex-changer technology allows for improved per-formance over metals and often makes thetechnology possible. In addition, ceramics canprovide better oxidation and corrosion resis-tance, which can result in longer component—

qTceramic bearings Cost about $100 while simi]ar steel bear-ings cost from $1 to $3,50.

aaRothman, et al., op. Cit., p. 191.@’Heat exchanger” is a generic term for any device that trans-

fer heat from a fluid flowing on one side of a barrier to anotherfluid flowing on the other side of the barrier. Here, the term refersto the use of such devices in combination with industrial fur-naces, stationary power generators, and engines.

lifetime. Constraints to the expanded use ofceramics in this application are those specificto individual types of heat exchangers, but in-clude the need for improved materials prop-erties such as thermal shock resistance and re-sistance to certain corrosive environments, thedevelopment of joining and sealing technol-ogies, and low confidence in the reliability ofthe ceramic components. The use of ceramicsis still not cost effective vis-a-vis metal alloysin some heat exchanger designs, especially forlarge industrial furnace and power systems,which are constructed from an array of thin-walled ceramic tubes, Processing technologiesare still being refined to provide high repro-ducibility for long (greater than about 8 feet)tubes. In addition, sealing against leakage be-tween the hot and cold streams has not beenfully successful.

Because of their high temperature and oftencorrosive environments, heat exchangers havebeen predominantly fabricated from stainlesssteels and superalloy; therefore, substitutionof ceramic materials will result in some sav-ings of chromium and cobalt, although theamount is difficult to quantify due to lack ofspecific end use reporting. On the other hand,much recent heat exchanger technology hasbeen made possible by new ceramic materials,and the resultant growth in the use of ceramicmaterials are not as replacement materials. Theuse of ceramic materials, such as high-tempera-ture cordierite (a magnesium alumina silicatecommonly referred to as “MAS”), silicon car-bide, silicon nitride, aluminum oxide, and lith-ium-alumino-silicate (LAS) in this applicationwill be driven by energy costs faced by usersand the unit cost of fabricating ceramic com-ponents.

The use of ceramics in recuperators, a typeof heat exchanger that allows a furnace to oper-ate more efficiently by recycling its waste heatto preheat incoming combustion air, has re-ceived a considerable amount of attention.Both development and commercialization re-search in ceramic recuperators was contractedby DOE’s Conservation Office through GTESylvania and the Carborundum Co. As a result,small ceramic recuperators are now commer-


cially available and are economically viable.They can be retrofitted to existing furnaceswith the modification of furnace burners tocope with the higher temperatures generated.The performance advantage of ceramic recu-perators is expected to encourage their use innew furnaces and as add-ens to unrecuperatedfurnaces; but a changeover in large industrialsystems will be slow owing to the high invest-ment costs of such installations coupled withthe current stabilization of energy costs. TheGTE “Super Recuper” is reported to save someindustrial furnaces 30 to 60 percent in fuel byenabling furnaces operating at 2,500° F to pre-heat incoming air to 1,600° F. Unlike the longtubular array systems, GTE’s counterflow platedesign heat exchanger does not present anymajor ceramics processing problems. But ma-terials properties improvements are needed inorder for the device to be applicable in certainhighly corrosive environments such as thosein the glass industry,

A variety of other heat exchanger applica-tions are being investigated by both the privatesector and DOE. They include ceramic regen-erator cores for inclusion in gas turbine enginedesigns and specific designs for use in cogen-eration and combined-cycle power generationequipment.

HEAT ENGINES

Ceramic materials are under active investi-gation by both the Federal Government and in-dustry for use in the propulsion of automobiles,trucks, military equipment (tanks and missiles),and aircraft as well as stationary uses, such aspower-generating equipment. Research in theseapplications is being conducted to achieve sig-nificant advantages over the use of metal al-loys, including fuel economy, improved per-formance, reduced maintenance, and possiblereduction of pollution emissions, with savingsof strategic materials a secondary objective.

Private sector R&D is focused primarily onadvantages of ceramics that could translateinto direct cost savings or improved productcompetitiveness. A review of the government-sponsored research in ceramic heat engines intable 7-11 shows that the main focus of that ef-

fort has concentrated on the gas turbine enginefor automotive applications.

The ceramic materials being applied todayto these technologies are generally termed“structural ceramics.” They include monolithicforms of the silicon carbide (SiC), silicon ni-tride (Si3N4), zirconia (ZrO2), and aluminum sili-cate (AlSi) families of ceramic materials. Ce-ramic composites are also being considered forengine applications because of their superiorstrength and hardness, low thermal expansion,and wear resistance, which may allow them toovercome the fracture problems of the mono-lithic ceramics. However, ceramic compositeshave been found to lose their strength at highertemperatures, a problem that has not yet beenresolved,

Ceramics are likely to see service in the hotsections of engines, progressively, as follows :50

●

●

●

●

●

●

●

Turbochargers: static parts and rotors,Small stationary electric power generators,similar to airplane auxiliary power units(APUs).Large stationary electric power generators,then mobile (ground and marine) APUs.Short-life turbojet and turbofan engines formissiles.Heavy-duty turboshaft vehicular propul-sion engines; military truck, tank, off-roadvehicular, marine engine.Automobile propulsion,Human-rated aircraft propulsion and util-ity electric power generation.

Technical advances gained from continuingresearch efforts are necessary before ceramicmaterials can serve in these applications.

VEHICLESCeramic materials are being considered ei-

ther as direct substitutes for selected compo-nents of existing gasoline and diesel enginesor for use in engines designed specifically tobenefit from the properties of ceramic ma-terials.

Component substitution in gasoline enginesoffers only minor improvements in fuel econ-

Soparkinson, op. Cit.

298 • Strategic Materials: Technologies to Reduce U.S. Import Vulnerability

omy or power production over conventionalall-metal engines. As such, while selected com-ponents (cylinder liners and heads, exhaust andintake ports, valves, bearings) of such enginesmay be fabricated from ceramics, a “ceramicgasoline engine “ is not considered a possibil-ity, Ceramic diesel engines, on the other hand,can provide a 10- to 30-percent reduction infuel economy and improved reliability due tothe elimination of cooling systems. Since onlyminor amounts of strategic materials are usedin conventional engines, ceramic componentssubstitution can only marginally affect the useof strategic materials. One possibility, as yetunproven, is that the pollutants emitted by suchhybrid metal-ceramic engines will be lower,owing to higher operating temperatures, andthat strategic materials savings could occurwith a shift in the materials requirements (now,PGMs and chromium) consumed by automo-tive catalytic converter systems.

Turbochargers. —Turbocharger rotors, nowmade primarily of nickel-based superalloys andnickel-iron alloys, could be a significant near-term use of ceramics. This technology51 is oneof the few heat engine applications being in-vestigated with mostly private rather than gov-ernment funding and is driven by a desire tocombine the fuel economy of today’s small carswith the performance of yesterday’s larger en-gines, As this competition for greater fuel econ-omy/performance increases in the automotiveindustry, the inclusion of ceramic rotors in tur-bochargers may retard an otherwise growingmarket for superalloy. The main candidatematerial for ceramic rotors is silicon nitride.

The primary attraction of the ceramic rotoris the improved performance provided by itslow rotational inertia, which enables a quickresponse by the turbocharger at low enginerpms. The higher weight of metal alloys causesa delayed response called turbo lag. Secondly,there are expected material cost savings to begained from the use of ceramics, along with

sIA turbocharger, added to a standard internal combustion en-gine, pumps hot air (compressed by action of a turbine spun byhot exhaust gases) into the engine. Other options for fuel econ-omy are available through redesign of the standard engine toimprove its performance by reducing the amount of waste heat.

overall weight savings (providing additionalfuel economy). The high-temperature charac-teristics of ceramics are not a prime factor.

Two technical problems constrain massproduction of ceramic rotors for turbochargers:the difficulties in joining ceramics and metalsand uncertain reliability and reproducibility inmaterials processing. Nevertheless, ceramicturbochargers may be offered—to a limitedextent—by the Japanese automobile industrywithin the next few years. Two Japanese firmsreportedly began delivering sample turbocharg-ers to Japanese car companies in mid-1983 fortesting purposes. One of these firms announcedplans to begin production in late 1984 and pre-dicted that its ceramic turbines will be mass-produced within 3 to 4 years. The major U.S.turbocharger manufacturer, Automotive Prod-ucts Division of AiResearch, competes in inter-national markets and expects to have its ce-ramic rotor turbocharger ready by 1986 for the1987 model year, If the ceramic turbochargeris successfully marketed by the Japanese indus-try, the U.S. automobile industry is expectedto compete by offering similar turbochargerson their specialty market automobiles, wheresuch gains in performance are desirable andthe consumer may be willing to absorb addedcosts (both initial and maintenance).

The ceramic turbocharger is seen as a pre-curser to the use of ceramics in gas turbine en-gines where the rotor must withstand higherstresses. Successful commercialization of theceramic turbocharger could provide valuableinformation to accelerate the application of cer-amics to gas turbine engines.

Gas Turbines and Diesel Engines.—Research in newautomotive engine designs to incorporate ce-ramic materials has been a major beneficiaryof government support. Technologies now be-ing investigated under contract to industry arethe “adiabatic” (or, minimum heat loss) dieseland gas turbine engines. Industry also supportsR&D in engine technologies through cost shar-ing on government contracts and its own pri-vate basic research. While various governmentprojects have been funded sporadically sincethe 1940s, the heaviest support has occurred


during the last decade.52 NASA was directlyinvolved in the early research with the Depart-ment of Defense and the Department of Energy(DOE) now taking the lead. The current majorprojects are DOE’s Automotive Gas Turbine(AGT) program to develop a gas turbine engineby fiscal year 1986 and the U.S. Army Tank Au-tomotive Command (TACOM) program withCummins Engine Co. to develop the adiabaticdiesel engine for use in military vehicles. It isbelieved that this diesel engine technology willeventually be transferred to the private sectorfor use in heavy-duty trucks. Automotive useof both the diesel and the gas turbine engines,if commercialized, is not expected until after2000.

The benefits foreseen in use of the adiabaticdiesel engine are increased fuel economy (dueto the reduction of lost energy and the elimi-nation of the need for a cooling system), reduc-tion in weight and inertia, and greater enginereliability and maintainability. Energy loss maybe reduced as much as 50 percent, and fuelconsumption, 25 percent over conventionaldiesel engines with a significant increase inpower.

The TACOM/Cummins research projectstarted with development of ceramic compo-nents for conventional diesel engines. A sec-ond phase followed to design and test anuncooled, nonadiabatic diesel engine with ce-ramic and metal parts. R&D is now proceed-ing on an adiabatic diesel engine, combiningboth a ceramic combustion system and a tur-bocompound unit (to utilize waste heat). Re-maining technical issues include the need forfurther materials research and the development

sZAc~ording to a draft interim report (November 1983) byCharles River Associates for the National Bureau of Standards,Technological and Economic Assessment of Advanced CeramicMaterials: A Case Stud~r of Ceramics in Heat Engine Appli-cations:

Since 1976, total U.S. Government support for R&D in ceramicheat engines has exceeded $10 million per year. In 1981, 74 percentof tota! go~.ernment fundin g was provided by DOE, 23 percent b yDOD, and about 3 percent by hTASA, In addition, Charles Ri\er Asso-[.iates ha~re estimated that private funding of structural ceramics R&D1s roughly’ equal to the amount of funding received by the prit’ate~ector from the government in this area. However, little informa-tion is available about the focus of this private funding, i.e., whatarnou n ts are devoted to heat engine applications.

of component manufacturing methods that arecost effective and provide reproducibility.

After Congress passed the Automotive Pro-pulsion Research and Development Act (TitleIII of Public Law 95-238) in 1978, DOE andNASA initiated the AGT program. Two con-tracts were awarded: one to General Motors(Allison and Pontiac divisions) for the AGT 100and another to the Garrett Corp. and the FordMotor Co. for the AGT 101. Each of these con-tracts involve the design, development, andtesting of an advanced ceramic automotive gasturbine engine. In the final versions the engineswill have been designed from scratch to exploitfully the material properties of ceramics. Sinceits inception in 1980, the AGT program hasbeen revised to take the development of the ce-ramic engine through to the proof-of-conceptstage. A probable decrease in funding in fiscalyear 1985 will require another shift in the over-all program goals or organization.

Both the AGT 100 and 101 have successfullypassed an initial testing phase. The modelstested were designed using ceramics for staticcomponents, retaining metal for rotary parts.The phase now underway will test versions de-signed with ceramic rotary parts.

One of the largest technical problems fore-seen with the application of ceramics as enginecomponents is that of gaining reliability andreproducibility in the large-scale productionthat commercial automotive application will re-quire, The ultimate phase required for bridg-ing a tough attitudinal barrier (“ceramics arebrittle”) and to ensure transfer of this new en-gine technology will be to convince engineers,designers, the automobile industry manage-ment, and consumers that ceramics can indeedserve in these capacities. This will require rig-orous testing of ceramic engines in real en-vironments—in automobiles subjected to dailyuse over long periods of time.

Again, the benefits of strategic material sav-ings from these new automobile engines willbe minor except for the possible changes inmaterials now used for catalytic converters. Re-sults from the use of advanced ceramicmaterials in vehicle applications and the knowl-


Photo credit A//isorJ Diw.won, Genera/ Mofors

Ceramic components are being evaluated in the advanced gas turbine being developed by Allison Division of General Motorsfor the U.S. Department of Energy and NASA

edge gained in processing of those materialswill undoubtedly benefit the development ofaircraft gas turbine engines, where real stra-tegic materials savings may be realized fromthe substitution of ceramics for superalloy(chromium and, especially, cobalt).

AIRCRAFT TURBINE ENGINES

The use of ceramics in gas turbine enginesfor human-rated aircraft is believed to be oneof the most challenging and difficult applica-tions for advanced materials, owing to highperformance demands and the extremely highrisk of use involved. It is, however, an area inwhich the private sector is acutely interestedbecause of a continuing desire to increase the

performance of jet engines. This performance,which translates into fuel economies, increasesas the inlet temperatures for a gas turbine en-gine increases. The current materials—super-alloys—used in the hot sections of the enginehave operating limits over time of about 1,9500F. Ceramics, on the other hand, can withstandoperating temperatures up to about 2,500° F.This higher thermal efficiency allows for a re-duction in airflow through the engine and acorresponding smaller engine size. NASA hasestimated possible introduction of monolithicceramics as turbine blades in this applicationaround the year 2010.53

Ssparkinson, op. cit.

Ch. 7—Substitution Alternatives for Strategic Materials

Both the Air Force and NASA54 have main-tained a continuing interest in ceramic gasturbine engine development, In the privatesector, both Pratt & Whitney and General Elec-tric Co. have contributed to basic research onstructural ceramics for potential aircraft engineapplications. The Air Force Materials Labora-tory has sponsored small research programs onthe evaluation of ceramics and ceramic com-posites with potential use in aircraft systems.NASA’s Lewis Research Center, in addition tomanaging DOE’s AGT programs, has sponsoredsmall research programs on structural cer-amics. NASA has also developed an overallprogram to augment its current research effortsin ceramics. This program, with its focus onthe aircraft engine, is intended to broaden thetechnological base of advanced ceramics by co-ordinating research in the various technicalneeds (e. g., materials processing, nondestruc-tive testing, design methodologies). The devel-opment of this plan was coordinated with othergovernment agencies and industry but was notincluded in the final NASA fiscal year 1985budget proposal.

Much work remains in developing mono-lithic ceramics and processing techniques andgaining applications experience before thesematerials will be acceptable for human-ratedaircraft. The advantages of ceramics with re-gard to engine performance and, to a lesser ex-tent, the potential for reducing the overall useof first-tier strategic materials are incentivesthat will help promote the still-substantial re-search, development, and commercializationtasks ahead.

STATIONARY ENGINESStationary engines being considered for ce-

ramic materials applications are primarily gasturbines for industrial and household use, in-cluding accessory power units for emergencyor peak load service. The possible developmentof these small generators for near-term usehave benefited from research sponsored by

s~The budget for NTASA’s Ceramic Technology for AerospaceHeat Engines was an estimated $3.3 million in fiscal year 1983and $4.4 million in fisca] year 1984.

● 3 0 1

DOE and the private sector. In the longer term,both General Electric Co. and Westinghouseare investigating the application of advancedceramics in large gas turbines for electric pow-erplants. It is believed that the thermal efficien-cies obtainable with the use of ceramics canresult in considerable energy savings. To beeconomic, the ceramic materials will have towithstand long component lifetimes. Theselarge units are not expected for use until 2000.Strategic materials savings could be realizedthrough reduced use of wear- and corrosion-resistant materials, such as chromium alloysteels.

Composites

Two or more materials, when combined intoa composite, can yield a product with very im-pressive properties, including high strengthand stiffness, low weight, and good corrosionand chemical resistance. In addition, compos-ites offer engineers unparalleled opportunitiesto tailor materials to particular applications.Most composites contain little or no strategicmetals, As a result, the anticipated growingmarket for composites has the potential to dis-place some strategic metal use.

Technically, a composite is any materialcomposed of two or more physically distinctphases. This category includes, among othermaterials, filled plastics, laminated materials,dispersion-strengthened alloys, and fiber-rein-forced materials. Of these, the latter two aremost likely to affect strategic materials usage.Dispersion-strengthened alloys were coveredin the superalloy substitution section, so thediscussion here will be limited to fiber-rein-forced materials (commonly called advancedcomposites). The basic characteristics of fiber-reinforced composites are outlined in box 7-B.

Advanced composites can be made from sev-eral different combinations of matrix and rein-forcement materials, but are generally clas-sified by matrix material. Table 7-12 shows themost common matrix and filament combina-tions. Organic (polymeric) matrix composites(including fiberglass reinforcements) are theonly composite materials in widespread com-


Box 7-B.--Fiber-Reinforced CompositesFiber-reinforced composites, which are continuous filaments or whiskers embedded in a binding

matrix, exhibit properties that exceed those of its constituents taken alone. Each constituent servesa special function. The filaments provide the strength and stiffness, while the matrix provides thebody of the finished composite product and transfers the stresses and loads to the fibers.

The mechanical properties of a composite depend on the composition of both the matrix andthe fibers, the relative proportion of each, the orientation of the fibers, and the length of the fibers.By varying these parameters, the strength of a composite can be optimized for the loads encounteredduring its service.

The filaments, which account for 25 to 80 percent of the composite by weight, can be eithercontinuous or discontinuous (whiskers). Composites with continuous fibers have outstanding direc-tional properties, while those with discontinuous fibers lend themselves more readily to such con-ventional metalworking operations as forging, extrusion, squeeze casting, and welding.55

In addition to strength and stiffness, the filaments enhance other properties of the composite.Often, the filaments will increase the maximum service temperature by adding high-temperaturestrength to the composite. Also, certain filaments can enhance thermal stability because they donot expand greatly when heated (i.e., low coefficient of thermal expansion).

Since most of the load-bearing responsibility falls on the fibers, the importance of the strengthcharacteristics of the matrix material is diminished. In fact, composites with the weaker, but lightermatrices such as plastics, carbon, and aluminum can have good strength. Therefore, compositesare known to have good strength and stiffness for their weight (i.e., high specific strength andmodulus).

The matrix provides more than the body of the composite. In unidirectional composites, whichhave all the filaments aligned in a single direction, the matrix provides most of the transverse (per-pendicular to the fiber direction) and shear properties. Additionally, the matrix is responsible formuch of the corrosion and oxidation resistance and for providing the visual and textural appear-ance of the finished composite product.

Although matrices and fibers serve different functions, they are not independent. The thermalexpansion mismatch between matrix and fiber must below to minimize thermal fatigue problems.Also, both phases must be chemically compatible at both fabricating and operating temperaturesin order to prevent interdiffusion and the concomitant degradation of fiber strength. In some caseswhere such compatibility is inconvenient, barrier coatings can be applied to the fibers to inhibitinterdiffusion.

SORobart R. Irving. “Metal Matrix Composite pose a Big Challenge to COnV9ntiOn~ mOYSt” 1- 4N, Jan. IZ, 19839 P. 35.

mercial use. Carbon/carbon composites are inlimited production for aerospace applications.Metal and ceramic matrix composites have yetto be commercialized, except in highly special-ized applications.

prospects for composites to displace strate-gic materials varies by composite class, Or-ganic or polymeric composites—the only com-posites now in widespread use—will seldomdirectly replace the first-tier strategic materialsconsidered in this report, but the indirect ef-fects of their use could be significant, as was

brought out at a recent National Science Foun-dation workshop:

It is unlikely that this country will witnessany wholesale and direct substitution of com-posites for critical and strategic materials un-less some national emergency dictates suchsteps. Rather, composite materials will makeinroads in those areas where weight and/orcost are the primary drivers. Most of the criti-cal materials, namely cobalt, chromium, plati-num, tungsten and tantalum are used becauseof their unique resistance to high temperature,

Ch. 7—Substitution Alternatives for Strategic Materials ● 3 0 3

Table 7-12.—Advanced Composite Materials Options

NOTE Circles ind!cate composites which have been or are now In production status

SOURCE Stanley L Channon, /ndustria/ Base and Qua/IfJca/Ion of Composfte Mater(a/s and .SWctwes (An Execut/ve Overview) (Alexandria. VA. Institute for DefenseAnalyses, March 1984), working paper, p 3

corrosion or their catalytic phenomena. In noway can the composite materials we ordinar-ily consider, graphite, glass, or Kevlar with ep-oxy, polyimide, or thermoplastic resins be con-sidered for direct substitution. The impact ofcomposites will come indirectly in secondaryeffects. An example is a gas turbine in whichthe weight reduction by the use of compositesfor stationary, low-temperature componentswill cascade into downsizing of high-tempera-ture components and result, not in eliminationof the critical metals, but in a significant re-duction in the amount of strategic materialneeded. se

Carbon/carbon composites, used primarily inaerospace applications, may also have indirecteffects on strategic materials through redesignof products. Metal and ceramic/glass matrix

S“William E. Winters, “Use of Composites in High Perform-ance Structural Application s,” Materials and Society, vol. 8, No.2, 1984, p. 313.

composites may eventually be used in veryhigh-temperature superalloy applications.

The high cost of advanced composite mate-rials is an important deterrent to their wide-spread use. Table 7-13 shows the high relativeraw material costs of various advanced com-posites. Moreover design, fabrication, testing,and inspection costs are often higher for com-posite materials than for monolithic materials.These costs can be expected to decrease as thematerials come into more widespread use andas processing and fabrication problems areovercome. Figure 7-3 shows the decrease ingraphite fiber costs since 1970.

The advanced composites industry has rap-idly become internationalized, with the UnitedStates, Japan, Great Britain, France, and othercountries participating in individual segmentsof the industry. Very often, separate fabrica-tion steps needed in the manufacture of par-


Table 7-13.—Price Range of Selected Composite Raw Materials

1985Reinforcement cost/pound

Graphite grades:Rayon precursor fibers (woven cloth) . . . . . . . . . . . . . . . . . . . . ., . . $70 to $80PAN precursor (commercial and large-volume

aerospace orders). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $17 to $40Pitch grade (high-volume aerospace) . . . . . . . . . . . . . . . . . . . . . . . . $35 to $275Graphite fiber prepreg (PAN grade, 60 percent fiber) . . . . . . . . $36 to $40;

up to $100/lb forspecialty products

Boron:Tungsten core. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $365 to $375

Boron fiber prepreg (carbon core fiber):250° cure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $270 to $300350° cure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $310 to $340

Kevlar:Type 29 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $5.40 to $39.25Type 49 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $12.55 to $48.20

SOURCE Va~ous Industrial producers contacted ~ythe Offlceof ~chnology Assessment

;970 1975 1980 1985

Years

SOURCE1970.1980d ata: Commercia/ Opportunities for Advanced Composites,A A Watts (ed)(Philadelphla, PA. American Society for Testing andMaterlals,1980), publication 704,p 90; 1985data provided bylndustryproducers.

ticular composites are undertaken in separatecountries. Although advanced composites arenot strategic materials in the ordinary sense ofthe term, a growing concern in the defensecommunity concerns U.S. dependency on for-eign processing capacity to fabricate key com-posite components. Until recently, for exam-ple, the United States depended on Japan andGreat Britain for virtually all carbon fiber rein-forcements made from polyacrylonitrile (PAN),one of three possible precursor materials forcarbon fiber. The United States now producessome carbon fiber using foreign PAN precur-sor materials. Also, Union Carbide has opened

a domestic PAN production facility that re-duces U.S. dependence on foreign PAN to 70percent of domestic needs. However, this do-mestic precursor is not yet qualified for all de-fense programs, so in many critical applica-tions dependence on foreign supplies is stillnear 100 percent. France, similarly, is thesource of all quartz fibers and of an importantcuring agent used in epoxy resin formulations.57

It has been estimated that, in most segmentsof the composites industry, U.S. production ca-pability could be doubled within 2 years if theneed arose.58

Polymer (Organic) Matrix

Polymers, such as polyesters, epoxies, andpolyamides, are by far the most developed ofall composite matrix materials. They are mostfrequently reinforced with (fiber) glass, graph-ite, or aramid (commonly referred to by itsDupont tradename, Kevlar) filaments. Poly-meric composites can have performance capa-bilities that are commonly thought unattaina-ble by plastics. For example, polyimidecomposites are capable of continuous opera-tion at 7000 F in some applications. Organic

Szstan]ey L. Channon, Industrial Base and Qualification ofComposite Materials and Structures [An Executive Overview)(Alexandria, VA: Institute for Defense Analysis, March 1984),p. 10 (working paper).

‘eIbid., p. 16.


composites are attractive because they com-bine these good physical properties with light-weight and ease of fabrication. Consequently,these materials may reduce the need for stra-tegic materials—not via direct substitution, butthrough the cascading effects of downsizingand redesign allowed by the decreased weightand innovative fabrication.

The total U.S. consumption of polymer com-posites in 1982 approached 1 million metrictons (tonnes). Of this, 618,000 tonnes of poly-ester/glass (fiberglass) was the largest share,Additionally, 106,000 tonnes of reinforced ther-moplastics and 28,000 tonnes of epoxy resins(equivalent to approximately 90,000 tonnes ofepoxy-based composites) were consumed.59

U.S. consumption of composite reinforcingfilaments in 1982 was: glass, 280,000 tonnes;aramid, 900 tonnes; carbon (graphite), 800tonnes; and other, 10 tonnes,

Fiberglass-reinforced organics (which are notgenerally considered advanced composites)dominate current markets. High-volume appli-cations include boat hulls, plumbing and bath-room fixtures, and automotive body and trimpanels, which are often made from poly-ester/glass composites. Low raw material costsand automated, high-speed production proc-esses have made possible the widespread useof polyester/glass composites. Figure 7-4 showsselected applications for different fiberglasscomposites.

Because of their high price, use of other poly-mer composites has been largely limited to aer-ospace applications, sports equipment, and au-tomotive applications. Low-volume aerospaceapplications for polymer composites have in-creased since 1968, when an epoxy/ boron hori-zontal stabilizer for the F-14 jet was first usedon an experimental basis. In 1970, the GrumannCorp. approved this application for limitedproduction.

Since then, air frames, air panels, satellitestructures, and sporting goods have been builtfrom advanced composites, Table 7-14 shows

5e]Oe] Clark, ~ofen~jaj of Composite Materia]s to Replace c~ro-

mium, Cobalt, and Manganese in Critical Applications, O T Acontract report, 1984.

recent aerospace applications for advancedpolymeric composites. In each of these appli-cations, advanced composites were selected fortheir high specific properties. Specific proper-ties refer to common materials properties (e.g.,strength), normalized to the weight of the ma-terial. Organic composites have very goodstrength and stiffness for their weight and aretherefore said to have high specific strengthand stiffness.

Aside from polymer/glass composites, thepolymeric composites with the greatest poten-tial for continued growth appear to be epoxy/graphite and epoxy/aramid. Epoxy/boron (de-spite its early use) is no longer seen as promis-ing, owing to difficulties in processing the ex-tremely hard and brittle boron fibers, to highcosts associated with producing the fibers, andto effective competition from the graphite andaramid systems.

Carbon Matrix

A carbon matrix reinforced with carbon orgraphite fibers is commonly known as a car-bon/carbon composite. They are high-costmaterials used in specialty applications andare, for the most part, in early developmentalstages. To date, commercial applications in-clude rocket nozzles and exit cones, re-entryvehicle nosetips, and aircraft brakes. 60

These materials are very strong and tough,and have the potential for maintaining theseproperties at temperatures up to 4,5000 F.Moreover, carbon/carbon composites are verylight—somewhat less than 25 percent of super-alloy density and about 50 percent of ceramic(monolithic or ceramic/ceramic composite)density—dimensionally stable, wear resistant,and free of strategic metals,

There are, however, several disadvantageswhich must be addressed. Controlled environ-ments or impervious coatings must be used toprevent oxidation problems in high-tempera-ture applications, and special weaves of graph-ite fibers are needed to prevent surface fatiguecracking caused by low interlaminar strength.

eochannon, op. cit., p. 36.


Pressurebottles

SilosTubingPipeMissile

shells

Figure 7-4.— Fiberglass Composite Applications

I f Fabrics 1 I I I

IManufacturing methods and design

Nozzles I

RodsTubesShapesBuilding

componentsElectrical

appliancesStructural

BoatsSilosCar bodiesScootersMotorcyclesFurnitureTrucksHomesChemical tanksSwimming poolBath tubsPlumbing fixtures

SOURCE: Cornmerck?l Opportunities for Advanced Composites, A. A. Watts (cd.) (Philadelphia, PA: American Society for Testing and Materials, 1980), publication 704,p. 112.

In addition, carbon/carbon composites are veryexpensive as a result of the complex weavingprocedures, long processing times, and highenergy consumption involved in processing. Aswith most developing materials, the cost is ex-pected to decrease as the technology emergesand production rates increase.

Development work at NASA and in indus-try is aimed at reducing the high fabricationcosts of carbon/carbon composites. Improvingcomposite strength and stiffness and increas-ing the reliability of coatings and oxidation-inhibiting matrix additives are also goals of thiswork.

U.S. carbon/carbon composite use is expectedto grow rapidly, primarily because of defenseand aerospace needs. In 1982, an estimated200,000 pounds of carbon/carbon was con-sumed in the United States. One survey of gov-

ernment and industry experts found an ex-pected need for 800,000 pounds of carbon/carbon by 1990—-a quadrupling in demand inan 8-year period.61 As already discussed, someconcern exists about U.S. reliance on Japan formost of its carbon fibers made from PAN. Al-though rayon- and pitch-based carbon fibers ex-ist, PAN-based fibers are used in most currentapplications. Figure 7-5 projects defense andcivilian needs for carbon/carbon compositesthrough 1990; this may be an overestimate, dueto changed program priorities.

Ceramic/Glass Matrices

Monolithic ceramics and glasses are brittleand exhibit low fracture toughness. The tough-ness of these materials can be improved by

61The 1982 estimate and the 1990 projection were made byChannon, op. cit., p. 42.

——— ..——— - -—


Table 7-14.—Current Aircraft Applications for Advanced Composite Materials

Component Source Remarks

Wing:F-15 composite wing . . . . . . . .

C-5A leading edge slat . . . . . .

F-5 main landing gear door. . .737 spoilers . . . . . . . . . . . . . . . .

A-4 landing flap. . . . . . . . . . . . .

F-5 leading edge flap . . . . . . . .B-1 leading edge slat . . . . . . . .

Empennage:A-4 horizontal stabilizer . . . . . .

F-5 horizontal stabilizer . . . . . .

F-4 rudder . . . . . . . . . . . . . . . . .

DC-10 upper aft rudder , . . . . .

L-101 1 vertical fin . . . . . . . . .

Fuselage:A-7 speed brake . . . . . . . . . .

F-5 speed brake . . . . . . . . . . .

McDonnell Douglas

Lockheed-Georgia

NorthropBoeing

McDonnell Douglas

NorthropLockheed-Georgia

McDonnell Douglas

Northrop

McDonnell Douglas

McDonnell Douglas

Lockheed

Vought Aeronautics

Northrop

Graphite/epoxy used to form wing ribs and spars overmuch of the wing substructure; target weight savingsfor entire wing, 25°/0

Basic design is graphite/epoxy skins over aluminumhoneycomb core: weight savings, 22%

Weight savings, 36°/0Basic design is graphite/epoxy skins over aluminum

honeycomb core with aluminum and fiberglass fittings,edgemembers and ribs: 108 units (27 ship sets) havebeen fabricated and service tested: weight savings,15%

Basic design is graphite/epoxy skins over aluminumhoneycomb with aluminum edgemembers except for amolded graphite/epoxy actuator rib: weight savings,47 %

Weight savings, 32%Basic design is graphite/epoxy skins over aluminum

honeycomb core with aluminum and fiberglass ribs andtrailing edge close-out. Front beam is moldedgraphite/epoxy along with the leading edge structure:weight savings, 15%; cost savings, 35%

Basic design is multishear web/solid-laminate skinconcept; shear web constructions are bothgraphite/epoxy laminates and fiberglass core-graphite/epoxy skin honeycomb structure: weightsavings, 28%

Basic design is graphite/epoxy skins over aluminumhoneycomb core with aluminum close-out ribs, integralspar, and torque tube fitting: weight savings, 23°/0

Used graphite/polymide in leading edge spar; other high-temperature materials used were fiberglass olyimidehoneycomb core, boron/polyimide prepreg. titanium,and high-temperature adhesive

Graphite/epoxy rudder is 32 ft2 rib-stiffened-skin designmanufactured in a co-cured assembly; compositecomponent weight is 57 lb: weight savings, 37%

Graphite and Kevlar composite box beam and skins toreplace 9 x 25 ft primary structure; compositecomponent weight is 640 lb (17°/0 metals): weightsavings, 25°/0

Built-up molded laminate design using graphite/epoxyelements bonded with structural adhesive: weightsavings, 400/0

Weight savings, 23°/0CONVERSION FACTORS 1 ft] – O 1 m’

Ilb = O 45 kgIf ! = 03 m

SOURCE CornmercM Opporlunft~es focAdvarrced Cornpo.wfes, A. A Watts (cd.) (Ph!ladelphla, PA American Soc!ety for Testing and Mater!als, 1980), publication 704, p 104

reinforcing them with ceramic fibers to limit Most glass compositions (e.g., lead, quartz,the growth of cracks. Currently, glass matrix borosilicate, and boron oxide) have been rein-composites are more developed than their forced on a laboratory scale. They have beenceramic counterparts. Ceramic matrix compos- allied with a variety of filaments, including alu-ites are still confined to experimental applica- mina, silicon carbide, graphite, and tungsten,tions–-they are not currently used commercially, in order to improve their toughness and high-


800 -

600 -

400 -

200 -

0 1 I I 1 I I I 11982 83 84 85 86 87 88 89 90 1991

Years‘Th~~e e~tlrnates, reported ifl 1~, reflect anticipated ‘se ‘n ‘eaPons

systems, aircraft brakes, and engines at that time. Recent changes in programplanning indicate that these needs may be overestimated.

SOURCE: Stanley L Channon, /rrdustria/ Base and Qua/if/cation of CompositeMa?eria/s and Structures (An Executive Overview) (Alexandria, VA: In.stitute for Defense Analyses, March 1984), working paper, p 43

temperature strength. One promising exampleis United Technologies’ lithium aluminum sili-cate glass, reinforced with silicon carbidefibers, This material has roughly 10 times thefracture toughness of the unreinforced glass upto about 2,0000 F.

Ceramic matrices that have been examinedexperimentally include alumina, boron nitride,zirconia, silicon nitride, and silicon carbide,Reinforced with either inorganic materials ormetal wires, these ceramics could possibly beused in applications with temperatures exceed-ing 3,0000 F. As with glasses, ceramics arereinforced to improve their toughness. They donot, in general, benefit from any improvementin high-temperature properties.

Reinforcement of higher temperature ce-ramics has been relatively unsuccessful to datebecause of fiber strength losses due to fiber andmatrix interaction at high fabrication tempera-tures, fiber recrystallization, and fiber fracturedue to abrasion and stress during processing.As a result of these problems, NASA researchhas been redirected to ceramic composites em-ploying weak bonding between the fiber andthe matrix and to developing processing tech-nologies that employ lower temperatures andno pressing, Clearly, ceramic/ceramic compos-

ites will need substantial additional researchand development. They may eventually be usedfor turbine vanes, blades, and cases.

Metal Matrix

Metal matrix composites are relatively newstructural materials. Many metals, includinglead, titanium, stainless steel, magnesium, cop-per, nickel, and zinc, have been experimentedwith, but the most highly developed are alumi-num matrix composites. Virtually any metalcan be reinforced; benefits include increasedspecific strength compared to conventionalmetals, improved wear resistance, and higherallowable operating temperatures. However,the gains from reinforcement are often insig-nificant when compared with the costs.

Metal matrix composites are still primarilylaboratory materials. However, some success-ful commercial applications exist. Toyota Mo-tor Co. has developed an aluminum/aluminacomposite for reinforcing the piston ringgroove in production diesel engines and is de-veloping composite pistons and cylinder heads.In such applications, improved performanceis highly valued, and this has been the justifi-cation for developing metal matrix composites,Table 7-15 shows some potential commercialapplications of metal matrix composites,

Copper composites are under considerationfor use in transmission lines. Lead is reinforcedfor use in batteries because in certain applica-tions lead lacks the strength to support its ownweight. Aluminum matrices, containing boron,alumina, or silicon carbide fibers are designedto compete with titanium. Reinforcing an alu-minum alloy can raise its allowable servicetemperature by 2000 F, permitting its utiliza-tion in many applications where it otherwisecould not be used. Aluminum/graphite and alu-minum/boron composites have been developedfor use at 525° F.

Fiber-reinforced superalloy (FRS) technologyis under development in the NASA Metal Ma-trix Composite Program, The aim of this pro-gram is to develop the technology to fabricatean FRS turbine blade capable of operating ata surface temperature of 1,100° to 1,200° C


Table 7-15.—Potential Commercial Applications of Metal Matrix Composites

-..Application

Aerospace:Space structures. . . . . . . . . . .Antennae ., . . . . . . . . . . . . . . . .

Aircraft:Airplanes:

Pylons . . . . . . . . . . . . . . . . . . .Struts . . . . . . . . . . . . . . . . .Fairings . . . . . . . . . . . . . . . .Access doors . . . . . . . . . . . .Wing box . . . . . . . . . . . . . . . .Frames . . . . . . . . . . . . . . . . .Stiffeners ., . . . . . . . . . . . . . .Floor beams . . . . . . . . . . . . .Fan and compressor

blades . . . . . . . . . . . . . . . . .

Turbine blades . . . . . . . . . . .

Turbine blades

Helicopters:Transmission cases . . . . . . .Truss structures . . . . . . . . . .Swash plates . . . . . . . . . . . .Push rods. . . . . . . . . . . . . . .Trailing edge of tail

rotor blades

Automotive:Engine blocks .

Push rods . . . . . .

Frames, springsPiston rods . . . .Battery plates . .

Electrical:Motor brushes . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . . .

. . . . . . . . . . . .

. . . . . . . . . . . .. . . . . . . . . . . .

. . . . . . . . . . . .Cable, electrical contacts . . . .Utility battery plates. . . . . . . . .

Medical:X-ray tables, prosthetics . . . .Wheelchairs . . . . . . . . . . . . . . . .Orthotics . . . . . . . . . . . . . . . . .

Sports Equipment:Tennis racquets ... , . . . . . . .Ski poles . . . . . . . . . . . . . . . . . .Skis . . . . . . . . . . . . . . . . . . . . . . .Fishing rods . . . . . . . . . . . . . . .Golf clubs . . . . . . . . . . . . . . . .Bicycle frames . . . . . . . . . . . .Motorcycle frames . . . . . . . . . .

Textile industryShuttles . . . . . . . . . . . . . . . . . .

Other:Bearings . . . . . . . . . . . . . . . . . . .Chemical process

equipment . . . . . . . . . . . . .Abrasive tools . . . . . . . . . . . . .

Desired properties

lightweight, stiffnesslightweight, stiffness

lightweight, stiffness, heat resistancelightweight, stiffness, strengthlightweight, stiffnesslightweight, stiffness, strengthlightweight, stiffness, strengthlightweight, stiffness, strengthlightweight, stiffness, strengthlightweight, stiffness, strength

strength, stiffness, heat resistance,impact resistance

strength, stiffness, heat resistance,impact resistance

strength, stiffness, heat resistance,erosion resistance

lightweight, stiffness, strengthlightweight, strength, stiffnesslightweight, strength, stiffnesslightweight, stiffness, strength

lightweight, stiffness, strength

lightweight, heat resistance, strength,stiffness

lightweight, heat resistance, strength,stiffness

lightweight, strength, stiffnesslightweight, strength, stiffnessstiffness

electrical conductivity, wear resistanceelectrical conductivity, strengthstiffness, strength, corrosion resistance

lightweight,lightweight,lightweight,

lightweight,lightweight,lightweight,lightweight,lightweight,lightweight,lightweight,

lightweight,

—

——

stiffness, strengthstiffness, strengthstiffness, strength

stiffness, strengthstiffness, strengthstiffness, strengthstrength, flexibilitystrength, flexibilitystrength, stiffnessstrength, stiffness

wear resistance

aslc whisker andlor continuous SIC filamentbSIC whiskers only

Suggested composite systems

B/Al, B/Mg, Gr/MgB/Al, B/Mg, Gr/Mg

B/Al, SiC/AlB/AI, SiCa/AlB/Al, SiCa/Al, Gr/AlB/Al, SiCa/AlB/Al, SiCa/AlB/Al, SiCa/Al, Gr/AlB/Al, SiCa/Al, Gr/AlB/Al, SiCa/Al, Gr/Al

B/Al, SiCa/Al, Gr/Al

tungsten or tantalum fiber-reinforcedsuperalloys

directionally solidified eutectics Ni3Al-Ni3Cb, Ni3Al-Ni 3Cb-N i, Ni-Mo wire

Gr/Al, SiCa/Al

SiCb/Al

SiCa/Al, B/Al

Gr/CuGrlCuAl2O 3Pb, Gr/Pb, fiberglass/Pb

B/Al,, SiCa/AlB/Al, SiCa/AlB/Al, SiCa/Al

B/Al, Gr/Al, SiCb/AlB/Al, Gr/Al, SiCb/ALB/Al, Gr/Al, SiCb/ALB/Al, Gr/Al, SiCb/ALB/Al, Gr/Al, SiCb/ALB/Al, Gr/Al, SiCb/ALB/Al, Gr/Al, SiCb/AL

B/Al, Gr/Al, SiCa/AL

Gr/Pb

Al2O3/PbB / A l2O 3, SiC/Al 2O 3

SOURCE Commercial Oppotiun(fies for Advarrced Cornpos/fes, A A Watts (ed ) (Philadelphia, PA American Socfety for Testtng and Materials, 1980), publication 704, P 119.


(2,000° to 2,200° F). FRS development has beencarried out almost solely through NASA spon-sorship. With no end user deeply committedto the material, its development pace has beenslow.62

NASA’s development prototype is a cobalt-free (15 percent chromium) iron-based tungstenfiber-reinforced superalloy (TFRS). This exper-imental material has been successfully fab-ricated into a turbine blade, but has not yetbeen engine tested. Cobalt- and nickel-based su-peralloys can be used as a matrix material, butonly if a protective barrier is provided to pre-vent tungsten/matrix interdiffusion. Hence, thefirst FRS material likely to be commercializedwill probably be cobalt free.

In addition to their high-temperature prop-erties, TFRSs are good substrates for thermalbarrier coatings (TBC), which also raise enginetemperature capabilities. The thermal expan-sion coefficient of TFRSs is low compared tosuperalloy and approaches that of currentTBC. Such coatings applied to TFRS compo-nents would, therefore, show less tendency tospan (i. e., crack and flake particles off the sur-face) than they do with present superalloy,(Spalling problems prevent TBC from being ap-plied to present superalloy blade and vane airfoils.) Further, regardless of the application ofa TBC, the high thermal conductivity of TFRSspermits the use of simpler internal blade ge-ometries for cooling air, thereby lowering man-ufacturing costs,

Several major technical problems currentlylimit the prospects for widespread use ofTFRSs in turbines. The expansion coefficientof the tungsten fibers is approximately one-third that of the matrix. This induces thermalfatigue in a TFRS blade, considerably reduc-ing its life. Also, tungsten fibers oxidize rapidlyat turbine operating temperatures if exposedto the hot gas, Accidental exposure of the fibersin service could lead to rapid failure of theblade. At present, insufficient confidence ex-ists that the probability of such exposure canbe kept acceptably low, even with the applica-tion of a coating,

Ceramic whiskers and fibers also have beenused to strengthen metal matrices. Such rein-forcement is attractive because ceramic whisk-ers and fibers have high strength at ambientand elevated temperatures, high elastic modu-lus, good oxidation resistance, and low density,It has been found that ceramic reinforcement,usually as chopped fibers, can significantly im-prove the wear resistance of certain metals.However, results of research with both thewhiskers and the long single crystal fibers havebeen disappointing so far.

One of the major advantages of metal com-posites over polymer composite systems is thatthere is not as large a difference between trans-verse and longitudinal strength. Transversestrength in metal composites is essentiallyequal to the strength of the matrix metal. Anadditional advantage, which can be important,is that metal matrix composites are electricallyconductive.

Generally, the cost of metal composites is onthe order of 10 times the cost of the matrixmetal alone. Much of this differential is dueto the high raw material cost of the reinforce-ment. Also, processing complexities add sig-nificantly to the total cost. For this reason,metal matrix composites are only consideredfor applications where the value of their addedperformance is great,

Prospects for the Future

Advanced composites are now entering aperiod of rapid growth. Much of this increaseduse will occur in the transportation industry,where there are significant incentives to de-crease the weight and increase the perform-ance of materials. Over the next 10 years, theaerospace industry could represent over 50 per-cent of the total high-performance compositesmarket, Significant growth in the automobileand industrial sectors may occur in the late1980s.63

ezparkinson, op. cit. esclark, op. cit., p. 1.


Aerospace Applications

Most aircraft applications of composite ma-terials do not require high-temperature per-formance and can be satisfied by polymer oraluminum matrix composites in such applica-tions as airframe and structural parts. The useof aluminum matrix composites in these appli-cations represents the largest foreseeable mar-ket for metal matrix composites, The down-sizing and redesign, made possible through thereduction in weight, has the potential to reducestrategic materials usage.

Weight reduction in aircraft translates intofuel savings, lower operating costs, and in-creased profits for commercial aircraft; in-creased range, payload, and maneuverabilityfor military aircraft; and reductions in manu-facturing due to parts consolidation in bothcases. The impetus for substitution of compos-ite materials for conventional materials comesfrom market forces alone rather than from anydesire to substitute strategic materials. Con-stant economic pressure can be expected tostimulate materials innovation.

Metal matrix composites, like advancedceramics, ceramic composites, and carbon/car-bon composites also have some potential foruse in the jet engine industry, where the useof composite materials is expected to be per-formance- and market-driven. Cost considera-tions for jet engine materials will be of second-ary importance relative to the overall cost ofthe engine.

While substantial technical problems mustbe overcome, these advanced materials couldboost operating temperature above 2,500° F,far beyond even the most advanced superalloysnow under development, However, use ofthese nonmetallic materials is not expected byNASA for human-rated engines until after theyear 2010—roughly the same period as for ad-vanced ceramics.

Tungsten fiber-reinforced superalloys will,in all likelihood, be used in jet engines only inthe event of a prolonged crisis in the cobaltmarket. They have not satisfied important relia-bility criteria necessary for serious long-term

consideration as substitutes for conventionalsuperalloys or directionally solidified eutectics.They have not yet seen active operating serv-ice and would require a serious testing com-mitment before acquiring the confidence forindustrial implementation,

Today, carbon/carbon composites can be fab-ricated into forms that may be useful in the gasturbine for combustor liners, cases, afterburn-ers, and nozzles. A one-piece bladed turbinedisc has also been formed, Industrial-researchis at such an advanced stage for low- stress ap-plications that jet engine afterburners made ofcomposites could be in use in 5 years. High-stress applications are 10 or more years away.The complex qualification procedures used inthe composites industry could affect timing, aswell. These procedures are discussed in theconcluding section of the chapter.

Carbon/carbon composites, despite their ad-vantages in low-stress applications, cannot beexpected to satisfy high-temperature, high-stress requirements for jet engine applicationsfor another 10 to 20 years. Use of these materi-als will depend on developments in oxidationinhibitors and nondestructive testing methods,While materials prices are of negligible impor-tance when compared to the overall cost of anengine, efficient implementation of these ma-terials in jet engines will require a major over-all redesign effort that will be both costly andrisky, Industry seems to believe that govern-ment risk-sharing will be necessary to promotea rapid development of these novel tech-nologies.

It is not expected that engine blades will bemade of carbon/carbon composite materials,if only because reliability criteria for rotatinghigh-stress parts are far from met, and testinghas been far from sufficient. 64

Automotive Applications

Currently, all the major automotive manufac-turers have active development programs in-vestigating the use of advanced composites in

~4c]ark, op, cit., p. 75.


automotive structures. A wide variety of pro-totypes have been fabricated of advanced com-posites, including hinges, brackets, leaf springs,drive shafts, doors, and door guard beams.Many of these components have been testedin actual service over the last few years andhave been found to perform well. Compositeparts equivalent to steel parts in performancehave been built. Significant redesign of thesecomponents has been accomplished to takeadvantage of the design flexibility which com-posites offer. Table 7-16 shows the potential au-tomotive applications for Kevlar-reinforcedcomposites.

Composites will also see increased use in au-tomobile engines. Toyota has used aluminumreinforced with polycrystalline aluminum ox-ide fibers for the connecting rods in an exper-imental engine. Advantages of composite usein engines could include increased fuel effi-ciency, faster engine response, and reduced en-gine vibration.65

Large-scale use of composites by the auto-motive industry could occur as broader con-sumer acceptance, lower production costs, and

B6Meta] Progress, February 1984, p. 14.

Table 7-16.-Potential Automotive Applications forComposites of Kevlar 49 Aramid

Potential application Reasons for use

Leaf springs . . . . . . . reduced weight, stiffness, fatigueresistance

Transmissionsupports . . . . . . . . . reduced weight, stiffness,

vibration dampingDrive shafts . . . . . . . .

Bumper beams . . . . .

Radiator supports. . .Anti-intrusion

beams. . . . . . . . . . .

Wheels . . . . . . . . . . . .

Body parts . . . . . . . . .

reduced weight,strength

reduced weight,resistance

reduced weight,




stiffness, fatigue

stiffness, damage

stiffness

damage

damage

stiffness, damage

Clutch faces, brakelinings . . . ~ . . . . . . . strength, wear resistance, high

temperature, frictional propertiesSOURCE: Commercial Oppoflunfties for Advanced Composites, A. A. Watts (cd.)

(Philadelphia, PA” American Society for Testing and Materials, 1980),publication 704, p. 119.

design concepts lead to a general expansion ofcomposite materials markets and lower prices.Corporate Average Fuel Economy (CAFE) reg-ulations have been instrumental in creating anenvironment for novel new concepts of auto-motive designs and materials usage. However,these pressures have been relieved by automo-tive downsizing to meet CAFE standards in theshort run. If CAFE requirements become morestringent and make downsizing less profitablein the U.S. market, polymeric and metal ma-trix composites could be a very importantmeans of achieving weight reduction. Newauto body parts production and assembly tech-nologies, which are likely to affect the use ofcomposites in automotive structures, are ex-pected to see implementation over the next 10years. Use of composites in substantial quan-tities is not expected to increase before the1990s. The impact of composites technologyon critical materials (mostly chromium) will belargely indirect, through weight reduction andperformance enhancement.

Barriers to the Adoption of Composites

Composites have some major technical prob-lems which counter the attractiveness of manyof the properties described above and inhibitthe introduction and effective use of thesematerials. There is little doubt that many ofthese problems will be overcome as the tech-nology matures,

Use of composites in many potential applica-tions has been discouraged by the lack of estab-lished design practices and insufficient designdata, Additionally, when composites are se-lected for use, they are often used as direct sub-stitutes for conventional materials without re-design. The performance of composites in suchcircumstances is often less than optimal. Theimplementation of sophisticated computer-aided design algorithms promises to reducegreatly the complexity of designing for com-posite structures and allow more effective useof composites,

Another problem of composites is the highcost of raw materials, especially high-perfor-mance reinforcements such as boron, graph-

ite, and aramid. Prices for these reinforcementsrange from $20 per pound to well over $100per pound. For this reason, advanced compos-ites (those with specific properties exceedingsteel) are selected only for applications wheretheir special properties are highly valued.

Contributing to the high cost is the poorproductivity of composite product fabrication.Processing composites is generally labor-in-tensive and time-consuming. While innovativetechniques for automated, high-speed process-ing have been developed, their use is not wide-spread and is usually limited to forming specifictypes of goods. Moreover, once a nonmetalliccomposite is fabricated, the integrity of thestructure is difficult to assess without destroy-ing the component. This drawback is beingovercome with the advent of nondestructivetests based on ultrasound and laser holographyand with improved design procedures and in-creased experience in end uses.

Long-Range Order Intermetallic Materials

Materials in which two elements are ar-ranged in an ordered pattern throughout theentire crystal lattice are known as long-rangeorder intermetallics. Although there are manytypes of intermetallics, three families are par-ticularly interesting with respect to the use ofstrategic materials:

Nickel aluminizes , , ., ... , . . . . . . NiAl and Ni3AlTitanium aluminizes . . . . . . . . . . . . TiAl and Ti3AlIron aluminizes . . . . . . . . ., . . . . . . FeAl and Fe3Al

None of the above materials contains any co-balt or chromium, but other compounds couldcontain strategic materials. Very little informa-tion concerning long-range order materials ispublicly available, making it difficult to assessthe state of the technology or determine whenit will be commercialized.

Each of these six materials has low densityas well as excellent high-temperature stability,strength, and oxidation resistance. These prop-erties have been known for many years, but thematerials have seen little service because ofbrittleness problems. Their poor ductility, par-ticularly at low temperatures, results in fabri-

Ch. 7—Substitution Alternatives for Strategic Materials Ž 313

cation problems, low impact strength, and lowthermal shock resistance. Recent research,however, has shown that the ductility can beimproved by microalloying and thermome-chanical treatment, This raises the prospect ofusing the intermetallics in high-temperature ap-plications, such as gas turbines, where strate-gic materials are currently used.

Nickel Aluminizes

Single crystals of Ni3Al exhibit good ductil-ity, but polycrystalline Ni3Al is very brittle. Be-cause of the cost and inconvenience of singlecrystal-technology, monolithic Ni3Al is unat-tractive for most applications.66 Research atOak Ridge National Laboratory has demon-strated that small additions of boron (around0.05 percent) to the polycrystalline form re-moves the ductility problem.67 Microalloying(doping) with boron makes it possible to ex-trude, forge, and cold roll these materials, Inaddition to being fabricable, these boron-dopedaluminizes have tensile strengths that comparefavorably with those of Waspaloy, Hastelloy X,and 316 stainless steel.

Possessing high-temperature strength and ox-idation resistance, and adequate ductility andfabricability, boron-doped Ni3Al alloys have po-tential as structural materials. The aircraft gasturbine industry is beginning to evaluate thematerial for various applications. Polycrystal-line forms are being considered for discs—operating temperatures up to 1,250° C, or2,280° F, seem possible. Combustor liners andturbine vanes are other possible uses. A sin-gle crystal Ni3Al turbine blade is also of in-terest.

The good oxidation resistance of Ni3Al re-sults from the formation of aluminum oxidescales, which protect the alloy, Recent workhas shown that alumina-forming materials

88 NiaA] is most commonly known as the dispersion phase[gamma prime) that imparts high-temperature strength to nickel-based and iron-nickel-based superalloy.

5TC. T. Liu and C. C. Koch, “Development of Ductile PoIY-crystalline NiqAl for High-Temperature Application s,” Techni-cal Aspects of Critical Materials Use by the Steel Industry, Vol-ume 1113, NBSIR 83-2679-2, June 1983, op. cit.

38-844 0 - 85 - 11 , ~L 3


have excellent hot-corrosion resistance in coalenergy conversion systems. Such findings sug-gest that aluminizes may be useful as structuralmaterials in sulfiding environments.

Titanium Aluminizes

The ductility problems of Ti3Al are overcomeby microalloying with columbium (niobium),a second-tier strategic material. Ti3Al is beingstudied in the United States for use in aircraftgas turbine engine compressor rotors and bladesand in low-pressure turbine discs, blades, andvanes. These materials are potential (albeit ex-pensive) substitutes for some superalloy (e.g.,Waspaloy and Inco 713.)68

Iron Aluminizes

Pratt & Whitney Aircraft has studied thesematerials in conjunction with rapid solidifica-tion rate processing.69 The inherent ductilityproblem was removed and an increase in ten-sile strength achieved by microalloying withtitanium diboride (TiB2). The particular inter-est in these materials is for use as sheet forcombustor liners—up to temperatures of 1,800°to 2,0000 F. Iron aluminizes are also of inter-est for turbine discs, blades, and vanes at lowertemperatures, and for cases.

Nickel, titanium, and iron aluminizes are allin relatively early stages of development. Whilethey have shown great promise to date, muchremains to be learned concerning the full rangeof their material properties.

Rapid Solidification

Many new and potentially useful materialsare being developed using technologies that so-lidify molten alloys extremely quickly. Theserapid solidification (RS) technologies enablematerials engineers to improve current alloysand to explore previously unattainable alloycompositions and microstructure. The effects

~Parkinson, op. cit., p. 49.@@JoSeph Moore and Colin Adam, “Potential of Rapid Solidifi-

cation for Reduction of Critical Element Content of Jet EngineComponents, ” Conservation and Substitution Technology forCritical Materials, Vol. IZ, NBSIR 82-2495 (Springfield, VA: Na-tional Technical Information Service, April 1982).

of this new technology on the use of strategicmaterials are as yet unknown. As emphasizedin a 1983 NMAB study:

Work is continuing in the field of rapidsolidification and its applicability to the reduc-tion of strategic elements. Work to date indi-cates that this method of processing holdsmuch promise for attaining at least a degreeof independence from such elements as cobaltand chromium in various systems of alloys.However, it must again be emphasized that, forcritical alloy applications, the principal moti-vation in alloy and process development is theachievement of improved mechanical, physi-cal, or chemical properties, Whether the suc-cessful application of RS technologies will beaccompanied by a reduction of the use of stra-tegic elements cannot be foreseen at this time.70

Rapid solidification refers to the chilling ofmolten materials into solids at very high cool-ing rates. Materials are considered rapidlysolidified when they have been cooled fastenough to assume microstructure that cannotbe generated by conventional solidificationtechniques. Cooling rates obtained with RSprocesses are often on the order of millions ofdegrees Celsius per second.

Because of the heat transfer characteristicsneeded to attain the requisite high coolingrates, RS materials must have high surfacearea-to-volume geometries. This requirementlimits the shapes of RS products to powders,flakes, and ribbons. These are rarely used inthe as-cast form; usually, consolidation andmill working operations are needed. The cast-ing, consolidation, and mill working processesare described in box 7-C.

RS in Strategic Materials Substitution

A vast number of alloy systems have beenrapidly solidified in the course of scientific in-quiry, but commercial interest in RS has beenlimited to only a few classes of alloys. Of these,transition metal-based glasses and aluminum-,nickel-, and iron-based crystalline alloys seemto have the greatest commercial potential.71 In

PONMAB.406, op. cit., p. 68.

71J. V. Woods, “Rapid Solidification Processes and Perspec-tive Part I I,” Materials and Design, vol. 4, April/May 1983, p. 712.


general, glassy materials are most interestingfor their magnetic or electrical properties,while crystalline alloys are of interest for struc-tural applications. Some of the potential appli-cations of RS materials include:

Aluminum alloys for aerospace structures.RS aluminum would compete with polymeric-and, possibly, aluminum-matrix compositesand titanium in these applications.72 73

— .pZNatiOnal Ma@rialS Advisory Board, Rapidly Solidified (RS)

Aluminum Alloys—Status and Prospects, National ResearchCouncil, Publication NMAB-368 (Washington, DC: NationalAcademy Press, 1981). This unclassified document contains in-

Nickel alloys with abnormally high refrac-tory metal concentrations for gas turbines.

Steels with submicron-sized phase disper-sions for higher speed bearings.

formation which is subject to special export controls. It shouldnot be transferred to foreign nationals in the U.S. or abroad with-out a validated export license. Distribution is limited to U.S. Gov-ernment organizations. Other requests for the document mustbe referred to DARPA/TIO, 1400 Wilson Blvd., Arlington, VA27709.

TSC$ Blankenship, panel/Workshop on Critical Questions inRapid Solidification Processing, Rapid Solidification Process-ing, Principles and Technologies, III, Proceedings of the ThirdInternational Conference on Rapid Solidification, Reston, VA,1983.


Amorphous (glassy) eutectic iron alloys withunusual electrical and magnetic properties forpower transformers and magnetic applica-tions. Use of RS alloys with good magnetic per-meability coupled with high resistivity can cuttransformer core losses by 60-70 percent. Thiscan greatly reduce energy wastage duringpower distribution.74 75

Commercial use of RS is still limited primar-ily for cost reasons. Auto industry experts esti-mate it will be 10 to 15 years before the tech-nology reaches their area. Entry should besooner in aerospace where a lo-percent im-provement in strength-to-weight ratio warrantsa twofold to threefold increase in raw materialprice. T’ Based on information gathered at thefirst Workshop on Rapid Solidification Tech-nology held at the National Bureau of Stand-ards (NBS) in 1981, the NMAB concluded that:

The primary application of RS crystalline al-loys at this time are superalloy disks for air-craft engines and high speed tool steels . , , andnear-term opportunities for commercial appli-cations of RS aluminum alloys appear limitedto the aerospace industry. 77

Limited commercial acceptance notwith-standing, RS research enjoys substantial sup-port from industry. Pratt & Whitney Aircraft,with the considerable support of the DefenseAdvanced Research Projects Agency (DARPA),has played a major role in promoting RS alloydevelopment, Production of RS superalloy ma-terial has reached the level of a few thousandpounds per year and some discs made from RSmaterial have been incorporated into jet en-

74’’ Glassy Metals Move Into Production, ” High Technology,March/April 1982, p, 80,

75’4Glass-Like Metals Cut Cost and Energy Use, ” Machine De-sign, Apr. 26, 1984.

~Metal Progress, “Trends in Powder Metallurgy Technology,”January 1984, p. 58.

TTNationa] Materials AdvisorV Board, Rapid so~idificationProcessing, Status and Facilities;, National Research Council,Publication NMAB-401 (Washington, DC: National AcademyPress, 1982), p. 3. This unclassified document contains infor-mation which is subject to special export controls. It should notbe transferred to foreign nationals in the U.S. or abroad with-out a validated export license. Distribution is limited to U.S. Gov-ernment organizations. Other requests for the document mustbe referred to DARPAITIO, 1400 Wilson Blvd., Arlington, VA27709.

gines.78 79 If processing difficulties can be over-come, it is possible that the suitability of differ-ent RS alloys for other engine applicationscould be determined in 5 years (with an ex-penditure of $5 million for each application).80

Cobalt-free superalloy powders producedthrough various rapid solidification processeshave been shown in early experiments to havesome advantages over conventionally proc-essed alloys. One promising example is an ex-perimental, cobalt-free superalloy being devel-oped by Pratt & Whitney Aircraft for turbineairfoils. The alloy, which chiefly containsnickel, molybdenum, and aluminum, offers su-perior creep resistance compared to someother hot-section alloys. Moreover, with addi-tion of 3 percent chromium as well as smalleramounts of hafnium and yttrium, the RS alloyhas oxidation resistance exceeding that of al-loy 454 (10 percent chromium), now used inthe turbine blades of the F-100 jet engine. TheRS alloy “offers approximately 1500 F advan-tage in temperature capability over our current(directionally solidified polycrystalline) metalsin the stress range critical for blade design.”81

Depending on the design strategy, the increasedtemperature capability can be used to improvethe performance, durability, or cost of the en-gine. R&D with this RS superalloy continues,but neither the results nor an estimate of thepossible year of introduction are available.82

The development of rapidly solidified iron-based alloys has received support from DARPAand the Army Materials and Mechanics Re-search Center (AMMRC). These two organiza-tions have sponsored a program at MarkoMaterials Inc. aimed at developing RS iron-based alloys for potential high-temperaturestructural applications in the intermediate tem-perature range of 800° to 1,200° F. These new

TWMAFMO1, op. cit., p. 16.Tgcharles River Associates, New Metal Processing Technol-

ogies, OTA contract report, 1983, p. 53.aOJohn K. Tien and Robert N. Jarrett, Potential for the Devel-

opment and Use of New Alloys to Reduce the Consumption ofChromium, Cobalt, and Manganese for Critical Applications,OTA contract report, 1983, p. 9.

alMoore and Adam, op. cit.azparkinson, op. cit., p. 48.


RS alloys will be specifically developed toevolve as potential replacements for conven-tional precipitation-hardenable (PH) stainlesssteels, titanium alloys, and iron-based super-alloys.83

Rapid solidification particulate technologyoffers great potential for the production of anew family of aluminum alloys that have prop-erties superior to those of ingot alloys. Accord-ing to NMAB, realistic property improvementslikely between 1985 to 1990 include: 10-percentreduction in density, lo-percent increase intensile strength, 15-percent increase in fatiguestrength, 10-percent increase in modulus ofelasticity (stiffness), and usable properties atelevated temperatures (450° F).84 Improve-ments in corrosion and stress corrosion crack-ing resistance are also likely. These alloys arenot expected to replace many strategic mate-rials directly. Furthermore, the new aluminumalloys may contain cobalt and manganese asalloying elements. However, RS aluminum al-loys will probably change the need for strate-gic materials because of design relationshipsin the applications where they are likely to beused.

Though actual in-service experience has notbeen accumulated, use of these new alloys isforeseen in a variety of aircraft, missile, ar-mored vehicle, and space structure applica-tions. Because of weight savings, significant re-ductions in fuel costs would be achieved, a’Effective use of the expected improved prop-erties will make these materials potentiallycompetitive with various composite materialsand titanium alloys for selected applications.

as~an jan Ra]~, vlsw~a nathan panchanathan, and Saul Isserow,“Microcrystalline Iron-Base Alloys Made Using a Rapid Solidifi-cation Technology, ’ Metals Progress, June 1983, p. 30,

84N MAB-S6B, op. cit, The improved properties of RS alum i-inure alloys derit’e from \’ery’ small grain sizes, extended solu-bilitj or supersaturation of solute alloying elements, and Ierjrfine dispersions of dispersoid and insoluble particles,

WA, [,. Bement and E, C, van Reuth, “QUO Vadis—RSR, ” RapidSolidification Processing; Principles and Technologies 11, R, Me-habrian, B. H. Kear, and M, Cohen (eds.) Baton Rouge, LA:Claitors [publishing [livision, 1980).

Near-term opportunities for commercial appli-cations, other than aircraft, are limited. Signif-icant commercial applications have not beenidentified, or at least verified, with any degreeof confidence. 86

Two RS aluminum alloys have achievedproduction status and are being offered as ex-trusions, die forgings, and hand forgings.These are alloys 7090 and 7091, air-atomized700()-series powder alloys that are modifiedwith cobalt additions and have been developedby Alcoa.87 The mechanical properties of 7090and 7091 have been evaluated in several indus-try and government programs. In addition togood strength and fracture toughness, these al-loys have excellent exfoliation and stress cor-rosion cracking resistance. This combinationof high strength and corrosion resistance is su-perior to that of any existing ingot alloy. Two7090 die forgings will be used as a main land-ing gear support link (an 85-pound finishedforging) and an actuator component for themain landing gear doors on the Boeing 757 airtransport. The components offer a 15-percentweight savings over the same parts designedwith conventional alloys. 88

The Air Force Materials Laboratory is cur-rently working on the development of advancedsecond-generation alloys with improved strengthand ductility properties, improved fatigue andfracture properties, increased modulus and de-creased density, and improved elevated tem-perature properties for service at temperaturesranging from 450° to 6500 F. Scale-up to pro-duction status will be initiated when adequateproperties are demonstrated and is expectedto be completed by 1990.89

WIN MA B-368, op. cit., p. 5.IW090 A]uminum—8. (1 7,inc—2, 5 Magnesium- 1.0 (kpper- 1.4

Cobalt7091 Aluminum—6,5 Zinc—2.5 Magnesium-1.6 Copper-O.4Cobalt.

‘8 Stephen Ashley, “RS Alloys Gaining A[;f:e[)tance, ’ .4n]eri-can Metal ~~arket, 9/12/83, p. 13.

aeNMAB-36u, op. cit., p. 2.


Institutional Factors in Substitution

The potential role of direct substitutes andadvanced materials in reducing U.S. strategicmaterial needs depends not only on resolutionof technical problems, but also on overcomingseveral institutional barriers that may impedetheir development. Several institutional issuesare discussed below, including the generalneed for improved material data management,qualification and certification processes in-volved in substituting one metal alloy foranother in critical applications, and factorsaffecting development of advanced ceramicsand composites.

Information Availability and Substitutes

Limited access to materials properties infor-mation inhibits the use of substitute and ad-vanced materials in many applications. Thelack of a publicly accessible material propertydata base not only discourages direct substi-tution, but also frustrates the design process.In a recent study on material properties datamanagement, the NMAB found that:

Materials properties combined with struc-tural analysis form the basis of modern indus-trial design. International competitive pres-sures are driving virtually all structural designin the direction of greater complexity and in-creased economies of production and opera-tion. If the U.S. industrial design process is toremain competitive in this environment, engi-neers must have rapid access to a well orga-nized materials properties data base.90

Handbooks, the traditional method of pre-senting material properties data, are increas-ingly unable to keep up with developments ina timely manner. Moreover, their methods oforganizing the data are too limited. The com-puterized material information sources that ex-ist are bibliographic services that search ac-cording to material properties. However, theinformation they provide is often cumbersometo use. According to NMAB:

,.. the citations for a given material are fre-quently so numerous as to render compilationand evaluation for relevancy a very time-con-suming and expensive task. Further, the inter-pretation of relevant data often is complicatedby the lack of a standard format for presenta-tion and the absence of sufficient informationto properly characterize the material.91

To make the most of the wealth of materialsinformation being generated, an on-line mate-rial properties data base with concise, thor-ough, and validated data would be desirable.This base would provide engineers with easyaccess to important information regarding sub-stitution and design. Benefits of such a system,according to the NMAB study, would include“stimulation of innovative design, decreaseddesign costs, and increased component relia-bility, and, as a result, the U.S. position in theinternational markets would improve.”92

Such an on-line data base would greatly en-hance the design process, especially that basedon computer-aided design (CAD) and com-puter-aided manufacturing (CAM) systems.Also, it would disseminate a great deal of use-ful information to small businesses, which maynot be able to support a staff of materialsengineers.

There seem to be no technical barriers to thedevelopment of such a data base. A recentworkshop sponsored by NBS, the Committeeon Data for Science and Technology of theInternational Council of Scientific Unions(CODATA), Fachinformationzentrum, and OakRidge National Laboratory (ORNL) found thatthe major problem is selecting the best orga-nization to lead the effort, raise the necessaryfunds, and coordinate the required technicalexpertise. 93

Finally, it should be mentioned that thedearth of easily accessible properties data is aparticularly acute problem for advanced ma-terials, such as composites and ceramics. The

WNational Materials Advisory Board, Materials Properties DataManagement–Approaches to a Critical National Need, NMAB-405 (Washington, DC: National Academy Press, 1983).

QIIbid., p. 3.‘JZIbid., p. 33.QaIbid., p. 3 and 102.


great potential of these new materials lies inthe innovative structural designs that theymake possible. However, in order to examinea wide array of structural configurations andto use most effectively the special capabilitiesof the materials, the design process must becomputer assisted, An on-line material prop-erties data base would be an integral part ofsuch a design system, However, not only aremachine-readable data not widely available,but information in any form is difficult to comeby. Much of the development work on ad-vanced materials is done by end users (as op-posed to suppliers) who have no interest inpromoting the material outside their companyor industry. Therefore, properties data are of-ten unavailable for use in other applications.

Qualification and Certification ofAlloy Substitutes

Currently, many promising alloy substitutesare under development that have potential toreduce strategic materials requirements. Actualuse of these materials by industry is problem-atic. Many of these substitute materials will notbe tested and developed to the point where theycan be considered on-the-shelf technologiesthat will be immediately available in a supplydisruption.

A major reason for this is that industry is notlikely to commit resources to qualify and cer-tify new materials that it does not have imme-diate plans to use. Qualification and certifica-tion is needed in many critical applications—those in which substitution could be most im-portant to reduced import vulnerability—yetfew substitutes will be taken through this proc-ess because of the time and cost involved. Thisbarrier appears greatest when there is no evi-dent economic driving force to entice indus-try to engage in the process. Such is the casefor many strategic materials substitutions—government, not industry, is the party with themost concern for making sure that the newalloy gains customer acceptance. In addition,owing to their critical applications, the certifi-cation process for strategic materials substi-tutes is more demanding of time and data,which translates into cost.

Two examples of alloy certification processes—one for stainless steel, the other for super-alloys—are discussed below.

Stainless Steel

As the earlier section on substitution pros-pects suggests, several promising low- or no-chromium alloys could serve as alternatives tocurrently used stainless steels and nonstainlessalloy steels. Actual use of technically promis-ing, lower chromium substitutes will dependon acceptance of these new materials by pro-ducers and end users. For many consumer anddecorative steel applications, substitution of anew material is a comparatively simple mat-ter—often entailing a decision to switch by amanufacturer. For critical applications, how-ever, extensive testing and certification is es-sential before widespread use.

In contrast to superalloys, in which com-pany-oriented qualification of materials pre-dominates, certification of new stainless steelsand alloy steels is usually undertaken throughcommittees of professional societies or tradeassociations, often through voluntary donationof time and facilities by producers and endusers, Such activities may take 10 years ormore if the immediate need is small, and canslow the process of user acceptance of replace-ment materials,

An instructive example of the steps entailedin qualifying a new material in a critical ap-plication is provided by the ongoing effort byDOE to qualify a new alloy as a boiler and pres-sure vessel material. The initial steps towarddevelopment of the alloy began in 1974, whena task force set up by DOE (then called theEnergy Research and Development Adminis-tration) recommended a program to developreference structural alloys for use in the liquidmetal fast breeder reactor.94 The alloy devel-opment process was sponsored through twooffices in the DOE under an Oak Ridge Na-

g4The history of the 9- I alloy is discussed in P. Patria rca, E.E. Hoffman, and G. W. Cunningham, “Historical Background”in P. Patriarca, compiler, ORNL Technology Transfer for A4eet-ing A New Chromium-Molybdenum Steel for Commercial Ap-plications (Oak Ridge, TN: Oak Ridge National Laboratory, Apr.7, 1982].


tional Laboratory contract with Union CarbideCorp., and in conjunction with CombustionEngineering, Inc. After studying several alter-native alloys, a modified 9Cr-1Mo alloy wasselected for further development, Data devel-opment for qualification began in 1979, but thealloy has yet to be approved for widespreadcommercial use. The purpose of the effort wasnot to conserve chromium, but rather to pro-vide a uniform construction material for boilersand pressure vessels. Figure 7-6 shows the de-velopment “ladder” for this alloy.

Once initial laboratory work had been under-taken, the need to demonstrate reliable trans-fer of properties through scale-up and field test-ing arose. Under arrangements with severalalloy producers, commercial heats (rangingfrom 0,5 to 15 tons) were made using severalcommonly used processing practices (e. g.,AOD and vacuum induction melting). Thecommercial heats were then formed into plates,bars, tubes, and pipes, using a variety of fab-

Figure 7-6.— Development of Modified 9Cr-1Mo Steelfor Fossil Fuel and Nuclear Power Applications

r

Foundation of knowledge of alloys A

SOURCE. John K, Tlen and Robert N. Jarrett, Potenfial for the Deve/oprnerrrand Use of New Alloys to Reduce the Consumption of Chromium,Cobalt, and Manganese for Crltlcal Applications, OTA contract

rication processes. To provide additional testdata, modified 9Cr-1Mo alloy replacements for18-percent stainless steel tubes have been putin service in six conventional powerplants lo-cated in the United States, Canada, and GreatBritain, as shown in table 7-17.

Widespread, nonexperimental use of thissubstitute in powerplant applications is depen-dent first on approval of its specifications bythe American Society for Testing of Materials(ASTM), followed by its inclusion in the Amer-ican Society of Mechanical Engineers (ASME)Boiler and Pressure Vessel Code,

In May 1981, an application was made toASTM to approve specification of the modified9Cr-1Mo alloy for use in plate and tube prod-ucts, followed a year later by a similar requestfor forgings, pipings, and fittings. The speci-fications are currently working their waythrough the ASTM approval process, as shownin table 7-18. A data package for inclusion ofthe material in the ASME Boiler and PressureVessel Code pertaining to nonnuclear applica-tions was provided in June 1982, Additionaldata will have to be collected before the sub-stitute material can be considered for possibleuse in nuclear powerplants.

By early 1984, the alloy had been approvedfor certain limited uses in conventional (non-nuclear) powerplants. Additional applicationsfor the alloy can be expected to be approvedsometime in 1985—9 years after initial designof the alloy. Estimated costs for the post-labora-tory alloy development through the end of 1983are $5 million by the government (an estimated$2 million has been donated in services by in-dustry).95

Superalloy

As suggested previously, several current andprospective materials and technologies couldbe used to reduce cobalt and, to a lesser extent,chromium use in the hot sections of gas tur-bine engines. Some, perhaps most, of thesemay have the technical potential to reduce stra-

osInformation provided by V. Sikka, Oak Ridge National Lab-oratory.report, September 1983.


Table 7-17.—Current Status of Testing of Modified 8Cr-1Mo Steel Tubes in U.S. and Foreign Steam Powerplants

OperatingTube temperature Tubes being Number Date

Utility Plant location (“c) replaced of tubes installed Status

Tennessee Valley Authority Kingston Steam Plant, Unit 3 Superheater 593 Type 321 8 May 1980 OperatingAmerican Electric Power Tanners Creek Unit 3 Secondary 593 Type 304 10 April 1981 Operating

superheaterDetroit Edison St. Clair Unit 2 Reheater 538 Type 347 2 February 1981 OperatingCentral Electric Generating Board (U K) Agecroft Power Station Superheater 590-620 2¼ Cr-1 Mo 6 April 1982 OperatingO n t a r i o H y d r o ( C a n a d a ) Lambton TGS Reheater 538 Type 304H 9 May 1983 Operating

Reheater 538 Standard 9 Cr-1 Mo 9Ontario Hydro (Canada) Nanticoke TGS Secondary 538 2¼ Cr-1 Mo 11 April 1984 Planned

superheaterSOURCE V K Slkka and P Patrlarca, L7a/a Package for Modlfled 9Cr-lMo A//oy (Oak Ridge, TN Oak Ridge National Laboratory December 1983), p 28

Table 7-18.–Status of Specifications for Modified 9Cr-1 Mo Alloy

Specificationnumber Description

A-213 T91 . . . . Seamless ferritic and austenitic alloy-steel, boiler, super-heater, and heat-exchanger tubes

A-387 GR91 . . . Pressure vessel, plates, alloy steel, chromium-molybdenum

A-182 F91 . . . . Forged or rolled alloy-steel pipe flanges, forged fittings, andvalves and parts for high-temperature service

A-234 WP91 . . . Piping fittings of wrought carbon steel and alloy for moder-ate and elevated temperatures

A-335 P91 . . . . Seamless ferritic alloy steel pipe for high-temperatureservice

A-336 F91 . . . . Steel forgings, alloy, for pressure and high-temperatureparts

A-199 T91 . . . . Seamless cold-drawn intermediate alloy-steel heat-exchangerand condenser tubes

A-369 FP91 . . . Carbon and ferritic alloy-steel forged and bored pipe forhigh-temperature service

Status as of December 1983

Approved and available as separate

Approved by Main Committee and await-ing Society Ballot




To be submitted for AI.06 Subcommitteeapproval



SOURCE: V K. Sikka and P Patriarca, Data Package for Modified 9Cr-lMo Alloy (Oak Ridge, TN: Oak Ridge National Laboratory, December 1983), p. 5

tegic materials without impairing the advancesin performance so critical to the military. How-ever, aside from those that are already fully de-veloped, most of these potential substitutes stillface massive R&D costs, and, if they prove via-ble, large scale-up and qualification costs.Given industry’s little incentive to assume thesecosts itself, unless clear performance and costbenefits would also accrue, most of the re-sources available for qualifying new super-alloy are dedicated to prospective materialsto be used in the next generation of jet engines.

Successful commercialization of a new su-peralloy for the hot section of a gas turbine en-gine can take two decades, beginning with theresearcher’s idea, through laboratory proof-of-concept, to engine testing and eventual com-

mercial application. Many research ideas neverreach the laboratory stage, and of those thatdo, only some show technical promise.

Even when technical problems can be over-come, institutional barriers can add appreci-ably to development time or can indefinitelydelay work on the project. Given the protractedtime period involved, what may have been ini-tially seen as a clear need for a new materialmay not be relevant a decade later. Many su-peralloy development efforts are cost-sharedbetween government and industry, which addsto the risk that R&D priorities will change dur-ing the course of the project. Coordination ofresearch may also be difficult. By the time com-mercialization of a superalloy is successfullyreached, several different government agen-


Photo credit: U.S. Oepatiment of the Interior, Bureau of Mines

Aluminum and silicon can reduce the need for chromium in stainless steels for high-temperature applications. A 5-percentaluminum addition to a Bureau of Mines 17Cr-8Ni research alloy (center) enormously improves oxidation resistance after380 hours at 1,000° C compared to type 304 (18Cr-8Ni) and type 316 (18Cr-12Ni) stainless steels. The research alloy is under

investigation as a possible high-performance alternative to the 25 percent Cr-20 percent Ni stainless steels

cies, universities, and companies may becomeinvolved—each with its own specific objec-tives, personnel, and priorities.

Typically, laboratory findings must be veri-fied in large-scale industrial heats. It is only atthis stage that the technical validity and man-ufacturing practicality of the process can beknown with assurance, and it is only at thisstage that the expensive and time-consumingprocess of engine qualification can begin.Designer and user acceptance of the new ma-terial will occur only when there is confidenceabout its reliability and performance at accept-able costs.

Figure 7-7 shows key steps that must be over-come in the successful commercialization ofa new superalloy, using Inconel MA 6000 asan example. Inconel MA 6000 contains no co-balt, but its initial development had nothing todo with conservation of strategic materials.Rather, the key objective was to develop a tur-bine blade material able to operate at a highertemperature than other superalloy, while

avoiding the performance penalties associatedwith the need for cooling air.

The origins of Inconel MA 6000 date backto 1968, with the invention by a researcher atthe International Nickel Co. of a mechanicalalloying process for producing oxide disper-sion strengthened superalloy. In 1974, NASAentered the picture by providing Inco with sup-port to design an alloy composition that be-came MA 6000. In time, university research-ers and several manufacturers of jet enginesbecame participants in the project as it ad-vanced through scale-up to its present status—preparation for engine testing. If successful, itwill probably be another 5 years before MA6000 is actually used for turbine blades andvanes in human-rated jet engines. Using 1974as a starting date, 15 or more years—and anestimated $10 million to $12 million—will havebeen consumed in the development of this onecobalt-free superalloy.

Development costs associated with an en-tirely new superalloy may be greater than for

— —— .


Figure 7-7.—Technology Transfer Ladder for ODS MA 6000

I

SOURCE Joseph R. Stephens and John K. Tlen, Considerations Of Technology Transfer Barriers in the Modification of Stra-t.9QiC Supera//oys for Aircratf Turbine Er?glrres, NAsA Technical Mernorarldurn 83395 (Springfield, VA’ NationalTechnical Information Service, 1983)

a superalloy with a modified composition. Forexample, the low- or no-cobalt COSAM alter-natives are intended as substitutes for existingsuperalloy. If the alternative materials werecommercially used, it is probable that only mi-nor adjustments in manufacturing and fabri-cation processes would be needed, In this re-gard, NASA’s proposed fiscal year 1985 budgetearmarks $50,000 for preparing several testheats of one of its four low-cobalt, alternativesuperalloy. Figure 7-8 shows steps taken todate and additional development required forthe COSAM superalloy.

Institutional barriers to continued develop-ment of the materials are formidable, even iftheir technical promise is favorable. In the caseof the low-cobalt COSAM alternative super-alloy, post COSAM augmentation effortscould require 6 to 7 years and $6 million to $9million, assuming real-time testing require-ments and typical scale-up activities for eachmodified alloy. Since the COSAM alternative

superalloy would substitute for already used,widely accepted, higher cobalt superalloy, nosingle company is likely to be committed to as-suming such a development effort simply forthe purpose of contingency planning for ahypothetical future cobalt shortage.

Institutional Barriers and Advanced Materials

Advanced materials face a number of institu-tional barriers before being adopted on a ma-jor scale. As comparatively new technologiesand new industries, they need the support ofmore complete and reliable data than is cur-rently available and of innovative design whichuses the materials to their best advantage. Inthe end, final acceptance of advanced materialsby engineers, designers, and consumers willcome only from experience in use. The Fed-eral Government’s efforts focused on these newmaterials can assist in this adoption processand promote the growth of new industries.

324 • Strategic Materials: Technologies to Reduce U.S. Import Vulnerability

Figure 7-8.—Technology Transfer Ladder for COSAMStrategic Material Substitution

SOURCE Joseph R Stephens and John K Tien, Considerations of Techrro/ogy Transfer Barr/ers in the Modification of StrategmSuperalJoys for Aircraft Turbfrre Engfnes, NASA Technical Memorandum 83395 (Springfield, VA Nattonal TechnicalInformation Servtce, 1983)

Ceramics Data Base Requirements, Standards,and Qualification Processes

The properties of ceramic components andthe materials from which they are made—andthus their usefulness for any particular ap-plication—can vary depending on their chem-ical formula and the methods by which theyare produced. One of today’s largest single in-stitutional constraints to expanded structuralusage of ceramics is the poor quality andlimited availability of information on thesevariable material properties. The technologyneeds not only the application of standardizedtest procedures (specific to materials and proc-essing and the effect of different temperatureand chemical environments over time) and asystematic collection of available informationbut also research efforts devoted to producingthe information.96

geThe National ~ureau of Standards recently announced theestablishment of a Ceramic Powder Characterization Labora-

Designer Preference and Education

Product design engineers select materials onthe basis of past experience and available data.Few structural design engineers have experi-ence with ceramics (less so with composites).As stated above, reliable data about materialproperties are scarce, and in general, formalcodes and specifications do not yet exist, Suchdata bases normally serve as guides for engi-neers working with unfamiliar materials,

In general, the formal education received byengineering students is deficient both in knowl-edge obtained about advanced materials andin how to incorporate that knowledge into de-sign work. For instance, materials courses arenot generally required of mechanical engineer-ing students, and if they are, the emphasis ison metals. Educational institutions are reluc-——tory (IVZ?S Update, June 11, 1984). The laboratory will help man-ufacturers by providing them with information on powder char-acteristics.


tant to adjust long-established curricula to elim-inate such deficiencies and may often be con-strained by budgets from doing so. In a broadercontext, the base of 10 to 15 universities in theUnited States with programs in ceramics maybe insufficient to meet the future researchneeds of a rapidly expanding industry,

Industry in Transition

The advanced ceramics industry is being cre-ated out of discrete parts of other industries.The mature traditional ceramics industry, con-servative because of a history of stable andprofitable years, is only now examining newpossibilities. This change in perspective maybe a result of recent depressed conventionalmarkets (linked to the steel industry) and talkof future competition from abroad. Most of theinnovations in the industry, however, appearto come from end users rather than from theproducers. Much of the research conducted byend users naturally leads them into becomingmaterials processors in order to maintain thenecessary tight control over this critical step.Other segments of this emerging industry arethe expansion into advanced ceramics by con-glomerates and conventional materials firmsthat sense future market changes.

This merging process means that there is nofocal point, no industrial champion for ad-vanced ceramics. As yet, no industrial associa-tion or organization is charged with research,development, or product data specification.The established professional association—theAmerican Ceramics Society—provides a forumfor the exchange of technical information. Itdoes not, however, have a technical sectiondealing with advanced ceramics as a separateissue. Recently, it has begun to collect data onindustry production of advanced ceramics andform a standardized data bank. With little in-formation yet available about the organizationof the industry and its participants, govern-ment data collection centers, such as those ofthe Department of Commerce,97 EPA, and

971 n f. rrnat iO n is hegi n n i ng to emerge, however. See, for in-stance, U.S. Ilepa rtrnent of Commerce, A Cornpetititre Assess-ment of the [;. S. ,4d\anced Ceramics lndustr~-, March 1984.

OSHA, do not yet aggregate advanced ceram-ics data separate from that of the traditionalceramics industry.

Government Research

Currently, several agencies are involved inmany aspects of advanced ceramics research:primarily, DOE, Department of Defense, NASA,and NSF. Those interested in the advancementof the technology express concern over the un-certainty from year to year over adequacy offunding, the direction of funding, and possi-ble lack of coordination which may lead toduplication of effort.

The bulk of the research effort is focused onthe high potential (in terms of market size,energy efficiencies, and strategic materials sub-stitution) heat engine applications. While thismay be appropriate from an applications pointof view, questions remain as to whether con-centration on major development projects isthe best way to advance the science of ad-vanced ceramics and whether this approachwill contribute to the building of a firm, broadbase of technical knowledge for the support ofa competitive domestic industry. Supporters ofthe concept argue that the technological baseis broadened by focusing on the developmentof a major application, since success requiresan iterative process in which researchers mustcontinually return to basic science in order tosolve problems encountered in the develop-ment phase. Others worry that, by pushing thedevelopment phase at the expense of basic re-search, application failures which occur willresult in generating negative impressions of theultimate capabilities of the technology.

The current contractors on the ceramic heatengine projects have plans to commercializethe technology eventually, but a technology gapwill exist after the proof-of-concept stage isreached by government R&D efforts. The skillsdeveloped in designing the ceramic compo-nents of experimental engines will be transfer-able to engines designed with the consumer inmind. But industry will have to be firmly con-vinced of the technology’s viability to be will-ing and able to take on expensive and lengthy


development costs before ceramic heat enginesare ready for the marketplace.

Until recently, there was no Federal officewith a specific mission to promote, coordinate,and focus the government’s R&D efforts in ad-vanced ceramics. (As is discussed in chapter8, the National Critical Materials Act of 1984establishes a council in the Executive Officeof the President that is to formulate a Federalprogram plan for advanced materials.) It is cur-rently difficult to obtain a comprehensive over-view of the R&D efforts of the various agen-cies and to determine whether there is anyoverlap of effort. Table 7-19 provides a break-down by agency of estimated Federal Govern-ment R&D for structural ceramics technology.This reflects internal shifts of program empha-sis and is a result of a growing awareness inmany sectors of the important role that ad-vanced ceramic technology could play in fu-ture U.S. economy.98

DOE has initiated some steps to cope withthe lack of available information. Its Oak Ridge

National Laboratory (ORNL), in its CeramicTechnology for Advanced Heat Engines Pro-gram Plan,99 provides a breakdown of the fundscommitted by various agencies for R&D in ad-vanced ceramics considered applicable to heatengine technology. The Advanced MaterialsDevelopment Program at DOE is developinga computer-based data system which, whencompleted, will provide continuing—and sys-tematically collected—information on the R&Defforts in structural ceramics of Federal Gov-ernment agencies.

Even with these statistics available, overlapof effort is difficult to assess. The difficulty lies,in part, in the large and growing number of ad-vanced ceramic materials, each designed withspecific properties for specific applications(similar to metallic alloys). While the knowl-edge gained from success in one application,if transferred, can advance the use of similarceramic materials in another application, a ma-terial designed for a specific application can-not necessarily serve “as is” elsewhere.

SeRobert B. Schulz, Program Manager, Advanced MaterialsDevelopment Program, Department of Energy, personal com-munication, Oct. 4, 1984,

W3ak Ridge National Laboratory, Ceramic Technology for Ad-vanced Heat Engines Program Plan, ORNL/TM-8896, June 1984.

Table 7.19.—Structural Ceramic Technology Federal Government Funded R&D (in millions of dollars)

Fiscal year Fiscal year Fiscal year Fiscal year1982 1983 1984 1985

Department of Energy:● Conservation and renewable energy:

— Heat engine propulsion . . . . . . . . . . . . . . . . . . . . . . . . . . .— Industrial programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .— Energy utilization research. . . . . . . . . . . . . . . . . . . . . . . . .

. Fossil energy:— Advanced research and technology development . . . . .— Advanced energy conversion systems . . . . . . . . . . . . . . .

“ Energy research:— Basic energy science . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

NASA:● Lewis Research Centerb. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

NSF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Department of Defense:● Defense ARPA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .● U.S. Air Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .s U.S. Army . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. U.S. Navy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Total . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

$ 9 . 31.50.3

1.21.9

2.0

1.8

2.7

2.01.71.31.0

$26.7

$14.61.00.5

1.0

3 . 0a

3.0

2.9

7.73.04.7C

1.2

$42.6

$15.52.30.6

1.0

3.0

3.5

3.3

9.53.46.0C

1.3

$49.4

$13.62.72.0

1.0

3.0

4.6

3.6

7.74.72.5C

1.4

$46.8aReflects increase in portion of budget applied to structural ceramics.blnclutjes salaries for manpower.CTACOM included.

SOURCE: U.S. Department of Energy, Advanced Materials Program, October 1984

Despite the lack of official oversight, coordi-nation among agencies has apparently im-proved in recent years. The ORNL programplan on ceramic heat engine technology wasdeveloped to identify technology base needs;develop a multi-year technical and resourceagenda; and coordinate activities with other in-dustry, government, and university programs.NASA holds regular and frequent meetingswith DOE that now include DARPA and theAir Force. Each fall, an interagency meetingis held for all the participants from govern-ment, industry, and academia working on cer-amics in heat engines,

NASA’s Lewis Research Center has also de-veloped a new comprehensive ceramics pro-gram proposal but funding was not includedin the fiscal year 1985 budget, The program’sgoal, while focused on the aircraft engine asthe application, was to broaden the ceramicstechnology base in general.

The National Science Foundation, under itsindustry and university cooperation program,has funded the Center for Ceramic Researchat Rutgers University. This center has beengranted public funding for 5 years with the in-tent that it will be able to generate sustainingprivate funding of its research efforts withinthat period. Research areas in which the Cen-ter is involved include, among other things,powder processing technologies and improve-ment of materials properties.

Qualification, Certification, and Standardizationof Composites100

Composites are engineered materials, and assuch are very sensitive to a multitude of struc-tural and processing factors. This character-istic is very beneficial, because it gives de-signers great control over the properties ofcomposites, allowing the tailoring of thesematerials to individual applications. However,

l~Thls section draws heavily on Stanley L. Channon, ‘ ‘Indus-trial Base and Qualification of Composite Materials and Struc-tures (An Executive Overview)” (Alexandria, VA: Institute forDefense Analysis, May 1984). Presented as a working paper fora Department of Defense-sponsored colloquium/workshop onComposite Materials: Standardization, Qualification, Certification,Washington, DC, May 1984,


with the greater design flexibility also comesthe need for strict materials and processing tol-erances during production runs, Addressingthe concerns arising from the sensitivity ofcomposites to each manufacturing step, thecomposites industry has adopted elaborate cer-tification and qualification schemes. These pro-cedures are needed to ensure the quality anduniformity of the various materials, through themany times they change hands, used in theproduction of composites.

Qualification and certification is more com-plex for composites than for traditional mate-rials for several reasons,

The composites industry is very fragmented–there is very little vertical integration. Thereare many processing steps entailed in the pro-duction of composites, and rarely, if ever, doesone company engage in all these segments ofthe business. Most composites companies arespecialized, each concentrating on a segmentof the industry,

While this may not increase the amount oftesting needed to ensure product quality anduniformity, it causes confusion with regard totesting needs and data interpretation.

Composites are fundamentally different intheir structure and behavior than traditionalmaterials. The well established testing andcharacterization techniques used for tradition-al materials are not suited for composites. Ap-propriate composites testing techniques havebeen developed, but on an ad hoc basis withlittle industrywide agreement.

There is no uniform procedure for certify-ing and qualifying composite materials andstructures; every product is handled differ-ently, on a company-by-company basis.

The composites industry has no industry as-sociation to pursue the interests of the compos-ites industry as a whole. There is no organiza-tion through which the industry can work onqualification, certification, and standardizationproblems common to many of the involvedcompanies.

Developing the data package necessary forqualification of composite materials and struc-


tures is very time-consuming and expensive(especially considering the small quantities ofmaterials often associated with compositeorders). The battery of tests required to qual-ify a material may cost $20,000 to $200,000 ormore, depending on the scope of testing. Whilethese costs are borne by the composites userfor the initial supplier’s material, alternate sup-pliers may be required to assume part or all oftheir qualification costs. The new suppliersmay be required to perform costly full-scaletests if bench-scale evaluation suggests signif-icant differences between their material andthe primary material. Qualification of a newsupplier for an existing material may require3 to 6 months for most structural applications.Whenever any change is made in the compos-ites used in rocket nozzles, full-scale test-ing—taking up to a year—is required. Thiscostly testing limits the number of suppliers forany given application.

In addition to being costly, the complexityof the qualification process may discourage in-novation. Once a composite has been qualifiedfor a particular use, changes in the material orits production are usually disallowed for thatapplication. This, along with designers’ pref-erence for proven materials, tends to restrictthe number of available qualified materials.

There is also a need for standardization ofmaterial specifications and test methods forcomposites, Standards are currently generatedby a variety of government and industry groups,but it is customary to rely on specificationsfrom fiber and resin suppliers. The governmentspecifications are rarely used because they aretoo broad or out of date. Industry groups suchas the American Society for Testing and Materi-als (ASTM), the American National StandardsInstitute (ANSI), the Society of Automotive

Engineers (SAE) and others generate compos-ites standards, but the process is slow and oftenincludes compromises accepted in order tobroaden the applicability y of the specifications.ASTM test methods find frequent use in indus-try, but many companies develop their own testmethods because of preferences in testingequipment and procedures.

Regarding the need for standardization ofcomposite materials, a recent industry surveyconcluded:

Although the majority of industry and gov-ernment personnel would prefer to see stand-ards adopted for the composites industry, it isrecognized that this will not be accomplishedeasily. A major resistance to standardizationemanates from the suppliers of materials whofear that the identity of their materials wouldbe lost. , . Some opponents to standardizationfeel that this would retard technological inno-vation in the industry whereas proponents feelthat the industry will advance more rapidly ifstandards are adopted. Some feel that the tim-ing is inappropriate for standardization be-cause the industry is still in a dynamic state. 101

Composites technology also faces other in-stitutional barriers similar to those for ce-ramics, although it is probably far ahead inmost aspects, The technology has found its ma-jor application in the aircraft and automotiveindustries and has been supported and pushedby those industries and by the government. Theextensive government research in compositeshas been centered primarily in the Departmentof Defense. The interest in composites for usein military aircraft, and the accompanying lackof public information, however, has been blamedfor slowing technology transfer between thegovernment, academia, and industry.

101 Ibid., p. 22.

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