Lecture 01 Manufacturing

7/29/2019 Lecture 01 Manufacturing

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UEET 601

Modern Manufacturing

Introduction to structure and propertiesof materials


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9/15/2013 UEET 601 Modern Manufacturing 2

Introduction What is manufacturing?

Conversion of a material from a primary form into amore valuable form - adding VALUE to a material

List examples ofANYTHING you know and how you

think they were produced

Involves product Design,

selection ofMaterials and

selection ofProcess


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Manufacturing demands/trends:

product design requirements, specs. and

standards environmentally conscious and economic

methods of manufacture

Quality issues flexibility in manufacturing methods

(Why?)

New developments in materials, methods,CIM

System dynamics, productivity


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Product design considerations:

product requirements and performance

design considered together with

manufacturing

product design cycle and life cycle

characteristics CONCURRENT ENGINEERING - integrated

product development and design:

CAD, CAM, CAE

Rapid prototyping

Design for manufacture and assembly


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What materials?

There are a wide variety of materials available

today with diverse characteristics that suitvarious applications. They are:

Metals and alloys

Ferrous or non-ferrous (Examples?)

Plastics Thermoplastics, Thermosets

Ceramics, glass and diamond

Composites

Engineered, Natural (examples?) Nano-materials, shape memory alloys, armorphous

alloys, superconductors


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Other considerations in the selection of

materials:

Properties of Materials Mechanical - how a material will respond to itsservice condition loading - strength, stiffness,

hardness, e.t.c.

Physical properties - density, thermal, electricaland magnetic properties,

Chemical properties - oxidation, corrosion, toxicity,

flammability

Manufacturing properties - machinability,weldability, formability, castability, heat treatment

Cost and availability

Appearance, service life and recyclability


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What Process?

A wide variety; usually a product goes through a

combination of processes Choice depends on properties of material and

product requirements, costs

casting - molten material allowed to solidify intoshape in a mold cavity

forming and shaping - rolling, forging, extrusion,

drawing, sheet forming, P/M, molding

machining - shape formed by removal of materialjoining - welding, soldering, adhesive joining, brazing

Finishing operations - polishing, coating, e.t.c.


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Structure of Materials


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The most important concept in

materials science

Structure Property Relationships

Composition

Processing

PropertiesStructure

Useful applications


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Compositionally Identical

Diamondhardest known material

transparent to light

electrically insulating

highest thermal conduction of

any material known

Graphiteone of the softest materials

known

opaqueelectrically conductive (in the

basal plane)

thermally conductive (in basal

plane)

Why? Processing, thats why.


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States of MatterGas molecules are free to move, no definite shape, no definite

volume container determines volume

Liquid - molecules are free to move but not as free as in a gas, definite

volume, no definite shape container determines the shape

Solids molecules cannot move freely, definite volume, definite shapePlasmas high temperature, similar to a gas, but many electrons are

free leaving many charged ions

*were going to forget about the Bose-Einstein condensate for this class.

While most industrial products are solids, liquids, or gasses, plasmas areimportant for industrial processing.


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BondingIonic electron transfer from one atom to another, bonding is

electrostatic, common in salts

Covalent electrons are shared by nearby atoms, common in

ceramics, semiconductors, and polymers

Metallic electrons in the valence shells become delocalized and areshared by the now positively charged metal atoms, common in

metals

Hydrogen bond this is an electrostatic bond between an

electronegative atom and a hydrogen atom bonded to nitrogen,

oxygen, or fluorine, important for water and for nucleic acid and

protein structuresVan der Waals bond a relatively weak bond caused by electric

dipoles, which in turn are caused by random motion of electrons,

occurs in all materials, important for noble gases, colloids (paint,

polishing and cutting formulations, etc.,)


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Structure of Materials - Metals

The vast majority of metals are crystalline (atoms have a regular

repeating spacing and orientation with respect to one another).

There are a number of different possible symmetries for atomic

arrangement, some common ones:

bcc fcc


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The 14 Bravais lattices

These represent the only

possible ways to stack hard,

uniform, spheres in 3-D

space. This is true for all

materials, not just metals.

Many more possibilities arise

when multiple atom types are

present.

* James F. Shackelford, Introduction to Materials Science for Engineers, Macmillan Publishing, 1988.


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Consequences of crystal structure:

FCC crystals have a close packed plane along the diagonal of the cube, it is

relatively easy to shear parallel to this plane.

In general fcc metals are more ductile, and have lower melting points than bcc

metals.

fcc planes can slip easily

bcc large corrugations, slippage is more difficult

Crystal structure also plays a very significant role in electronic properties, very

important for semiconductors.


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Formation of crystals:During cooling from a molten state crystal growth starts (nucleates) in

many different places, these nuclei grow until they run into one another.

Since the crystals nucleate in random

orientation, when they meet there will

be a boundary. These crystals are

called grains.

Most metals are polycrystalline,production of single crystals is possible

in many cases but requires specialized

processing.

* http://chemical-quantum-images.blogspot.com/2007/03/shaping-copper.html


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Defects in Crystals:Point

- Impurity (present in all materials)

- Thermally Generated

vacancies a missing atom

interstitialan atom in a position that isnt supposed to

have one

Line

- dislocationsPlanar

- twins

- grain boundaries


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Most are crystalline (except for glasses) and often polycrystalline, with

many grains like metals.

The difference is in bonding, covalent (or ionic) instead of metallic.

Much more difficult for dislocations to move, low ductility/brittle.Consider Al and Al2O3:

Structure of Materials - Ceramics

Al

Melting point 660 C

Mohs hardness 2.75

Electrical resistivity 2.65 x 10-6cm

Al2O3Melting point 2054 C

Mohs hardness 9 (about 100X harder)

Electrical resistivity 2.0 x 1013cm

Semiconductors are generally similar in bonding, but with greater ease of freeing

an electron.


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Structure of Materials -

Semiconductors

Silicon is FCC with two atoms per lattice

point, this is the same as diamond and

germanium. Diamond is not considered a

semiconductor because it requires too muchenergy to free an electron.

In most applications semiconductors are used

in single crystal form (no grain boundaries).

* wikipedia.org


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Structure of Materials -

Semiconductors

Conductivity of Semiconductors is modified by controlling defect populations.

Adding small quantities of anelement with one too many

electrons makes that extra

electron very easy to free.

Adding small quantities of an

element with too fewelectrons makes a missing

bond in the structure, this is

also easy to move.

* wikipedia.org


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Structure of Materials - Glass

Sometimes classified as a ceramic. A covalently bonded network that

does not have a well defined repeating structure, it is amorphous.

Generally formed by cooling a melt of mostly silica (SiO2) containing

other glass formers, intermediates, and modifiers (B2O3, P2O5, Na2O,CaO, Al2O3, PbO, etc.) fast enough that it cannot order itself into

crystals. Unlike in metals this is not difficult to achieve.

While there is no long range order there is typically short range order,

Si atoms are mostly bonded to four O atoms.

Melting point is not as well defined as in other materials, glasstransition temperature.


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Structure of Materials - Polymers

Covalently bonded chains, made from repeating monomer units

polymerization

C C

H

HH

H

C C

H

HH

H

C C

H

HH

H

n

ethylene polyethylene

Covalently bonded within

the chain, but with theability to twist.

Between chains bonding

can range from Van der

Waals to covalent cross-

linking

Catalyst, heat, light


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Structure of Materials - Polymers

Huge variety of polymer types

Addition polyethylene, PVC, pAA, pAMPS, polystyrene, etc.

Condensation polyurethane, nylon, polycarbonate, silicones, etc.

Can also be co-polymers (mixed monomer types, block or random, cross-

linked or not, etc.


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Mechanical, Physical, and

Manufacturing Properties of

Materials


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Mechanical Properties

Manufacturing often involves application of

external forces.

The response of a material to external

forces is important for its use in different

applications


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Types of Forces

Tension

Compression

Torsion Bending

Shear

Tensile testing is a common way to evaluatethe strength of a material, though other

types of testing are also done.


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Tension Test

A material loaded in tension will stretch.

L0

AF

A

Fstress

0L

Le

strain

units are force per area [Mpa, psi]

Dimensionless, expressed as in/in or %

What is the relationship between stress and strain? It depends on the material.


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Stress Strain Curves

*http://irc.nrc-cnrc.gc.ca/images/cbd/157f02e.gif


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Stress Strain Curves

*http://www.mech.uwa.edu.au/unit/MECH2402/lectures/hot_cold_working/degarmo_17-7.gif

Proportional, Hooks law,

Youngs modulus, E=/e


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Ductility

The extent to which plastic deformation

takes place before fracture:

Elongation

Percent reduction in cross sectional area

%100*i

if

L

LL

%100*i

fi

A

AA


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Hardness

Ability to resist permanent indentation from a

scratch.The result depends both on the material and on the shape of the

indenter, it is not a fundamental material property.

Wear resistance is related and sometimes tested

also with a sliding stylus or indenter.


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Hardness Tests

Brinell Hardness (BHN) uses a hard ball

indenterMultiple different sizes and materials can be used for the

ball

Vickers Hardness uses a diamond

pyramid indenter

Knoop (KHN) also uses a diamondpyramid

A microhardness test, for thin sheets

Rockwell multiple types of tests


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Fatigue

Components may undergo cyclic or

otherwise fluctuating loads that may cause a

part to fail at lower stresses than if under a

static load.

Its cause is the movement of dislocations

that eventually form small cracks which

weaken the material. Fatigue failure is responsible for the

majority of failure of mechanical

components.


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Creep

Permanent elongation over time under astatic load. caused by disslocation slipping, grain boundary sliding, anddiffusional flow

often worse at elevated temperature but that is materialdependent (W > 1000 C, ice even at sub-zero temps),typically 30% of melting temp for metals and 40-50% forceramics (glass does NOT creep near room temperature)

very important for high temperature applications nuclearplants, turbine blades, steam power plants, etc

also important for more mundane applications paperclips, light bulbs


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Impact Resistance

The ability to withstand impact loads. It is a

function of both ultimate tensile strength

and ductility (the area under stress-strain

curve)


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Physical Properties

Other physical properties are also improtant in

material selection and manufacturing decisions.

(examples)

Density

Melting point

Heat capacity

Thermal expansion

Thermal conductivity

Electrical conductivity

Magnetic properties (permittivity, magnetoresistance, magnetorestriction

Other dielectric properties (dielectric constant, breakdown strength)

Chemical compatibility/corrosion resistance

Optical properties

Specific properties are a


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Specific properties are aconvenient way to compare

materialsMaterial UTS

(Mpa)SpecificStrength

Stiffness(E, Gpa)

SpecificStiffness

Steel(SG = 7.8)

450 58 210 27

Aluminum

(SG =2.7)

150 56 70 26


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Density

Mass per unit volumeV

m

[g/cm3, lb/ft3]

Important for transportation. Strength (of the type required) per weight is

another way to look at this one.

Melting PointImportant for casting, refractories, others


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Heat Capacity

Energy required tochange temperature Tm

Qcp

[cal/gC, J/gC, cal/lbF]

Important for machining, forming, and thermal management, why?

Thermal ExpansionDimensional change

per unit temperature

iL

L

T

1 [1/C]

Important for stress management, expansion joins, glass metal seals, shrink

fits, thermal fatigue, etc.


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Thermal Conductivity

Rate at which amaterial can transport

heat.

[W/mK]

Important for machining, thermal management (extrusion, microelectronics, etc.)

Electrical ConductivityAbility of a material to

carry electricalcurrent, inverse of

resistivity.

RA

l

[1/ cm]

Important for electrical applications, examples?

Tx

AtQk

1


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Chemical Compatibility

This is a major issue that needs to be considered along with all of the otherphysical properties.

Examples: Corrosion in transportation (air, sea, land), refractories, bridges and

buildings,

Dielectric strength

Amount of applied electric field before failure. [V/cm]

Important in integrated circuits (driving away from SiO2 gates), electrical

insulation.


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Magnetic properties

Important in hard disk industry, transformers, RF processing, others?

Other properties

Piezolectric, ferroelectric, thermoelectric, magnetorestriction,

magnetoresistance. What might these be useful for?


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Changing Properties of

Metals, Heat Treatment and

Strengthening Processes


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Structure of Alloys

Alloy = composed of two or more types of

atoms, at least one of which must be a

metal. Both solid solutions and intermetallic

compounds are alloys.

Steel the most famous class of alloys


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Solid Solutions

What it sounds like, analogous to a solution

of liquids.

The solvent must maintain its original crystal

structure. Either because the solute can

occupy the same sites (with about 15% of

the same size), or because the solute can

occupy interstices.


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Intermetallic Compounds

Compounds that form between metals.

Rather than a solution in the same structure

a new structure is formed. Many are hard

and brittle. Fe3C is the most famous ofthese.


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Phase Diagrams

In pure metals solidification takes place at constanttemperature

Mixtures solidify over a range of temperature.

Phase diagrams show the EQUILLIBRIUM situation,

kinetics are not considered

* http://www.sv.vt.edu/classes/MSE2094_NoteBook/96ClassProj/sciviz/html/clicktuta.html


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The Iron-Carbon System

* Materials Science and Metallurgy,

4th ed., Pollack, Prentice-Hall, 1988

Polymorphic transformation

BCC to FCC (austenite)

Partial transformation to

ferrite (ductile and soft)

Transformation to ferrite

and pearlite (alternating

layers of cementite and

ferrite)


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General classes of steels

Low carbon (mild steels) 0.6% C hard, strong,brittle, tool steel, springs, cutting tools


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Heat Treatments

Both microstructure and composition affect

a materials properties. Heat treatment is

one way to manipulate microstructure.

These changes to microstructure are caused by phasetransformations and changes in grain size. These effects are

both thermodynamically and kinetically driven.


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Ferrous Alloys

Pearlite has a laminar structure whichcan be coarse or fine depending on the

rate of cooling through the eutectoid

temperature. Finer structures are

generated by faster cooling.

http://info.lu.farmingdale.edu/depts/met/met205/tttdiagram.html

http://www.matter.org.uk/steelmatter/metallurgy/7_1_2.html

Martensite a supersaturated solid

solution of carbon in iron, achieved by very

rapid cooling (quenching) from austenite.

has a laminar structure which can be

coarse or fine depending on the rate of

cooling through the eutectoid temperature.

Finer structures are generated by faster

cooling.
http://info.lu.farmingdale.edu/depts/met/met205/tttdiagram.htmlhttp://www.matter.org.uk/steelmatter/metallurgy/7_1_2.htmlhttp://www.matter.org.uk/steelmatter/metallurgy/7_1_2.htmlhttp://info.lu.farmingdale.edu/depts/met/met205/tttdiagram.html


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Ferrous Alloys (cont.)

Spheroidize anneal pearlite heated to just belowthe eutectoid temperature for a long period of time (1day) will transform the cementite laminar stuctures tospheres less stress concentration better ductilityand toughness

Tempering martensite is reheated to anintermediate temperature


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Other Heat Treatment

ProcessesAnnealing Used widely to restore ductility in cold worked

materials or in castings. Material is heat soaked to a specific range

of temperature for a period of time and allowed to cool slowly either

in a furnace or in still air.

In full annealing, there is microsturctural change due torecystallization, in a stress relief anneal the material is heated to a

lower temperature to reduce internal stresses.

Case Hardening a process where carbon is introduced to the

surface only, allows the underlying material to retain ductility and

toughness.


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Non-Ferrous Alloys

Non-ferrous alloys and some stainless

steels have completely different phase

diagrams from normal steels, thus they use

different heat treatments and mechanisms toalter properties.Precipitation hardening a 2-phase alloy is heated until it is

above its solubility limit and is then slowly cooled or held at

an intermediate temperature, precipitates will form in the

solid solution, these can interfere with slip propogation.


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Non-ferrous Alloys


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Introduction

Covers a very wide range of alloys

In general, more expensive than Ferrous

alloys but have other advantages

We will examine the most common

categories


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Aluminum and its Alloys

General properties very high specific strength

and stiffness

good corrosion resistance,

good formability easily formed into shape

good electrical conductivity

good thermal conductivity

Relevant Applications

transport industry, structural

parts (B747 = 82% Al)

containers and packaging

(cans, foils, etc), aerospace

cookware, aircraft skin

overhead power lines,

electrical applications

(integrated circuits)

heat exchanger tubes,

radiators

Alloys


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Alloys

Two categories: WROUGHT and CAST

Wrought:

formed into shape. Also has two categories:

Those strengthened by heat treatment

Those strengthened by cold working

Major applications: formed products, fittings, tubes, sheetmetal, rivets (Al/4%Cu - ages naturally)

Cast:

final component produced by a pouring molten metal into

a mold Most popular are the Al-Si alloys. Si promotes fluidity

during casting.

Used mainly for Aluminum castings of components e.g

engine parts (cylinder head), general Al castings


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Magnesium and its Alloys

Magnesium - the lightest metal for general engineeringapplications; possesses good vibration damping

characteristics

Cast or wrought

Typical applications in aircraft and missile components,materials handling equipment, portable power tools,

ladders, luggage racks, sporting accessories (weight),

textile and printing (lower inertial effects)

Pure Mg has low strength - alloyed to improveperformance Main alloying elements are Zn and Al

Good castability, formability and machinability


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Copper and its Alloys

Commercially pure Cu generally containsvery little alloying (e.g Phosphorous,

sulfur and oxygen)

Good thermal and electrical conductivity -

electrical applications, heat exchangers

Good formability - rivets, rolls, nails,

gaskets


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Alloys

Brass - Copper + Zinc; good ductility, corrosion

resistance and thermal conductivity. Used forradiators, ammunition catridges, plumbing, gears

Tin Bronze - Copper and tin. Good formability and

castability. Castings

Phosphor Bronze Cu + Sn + Phosphorous.

Phosphorous protects the melt from oxidation.

High toughness and low coefficient of friction.

Bearings, bushes, valves, clutch disks, springs.Cupro-nickels: Copper + nickel; ornamental

applications, coins, heat exchangers

Others - Aluminum bronze, beryllium bronze


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Nickel and its Alloys

Ni is ferromagnetic

Major element that imparts strength, toughness and

corrosion resistance -used extensively in stainless

steels High melting point (1455oC), high resistance to

oxidation at elevated temperatures

Generally used for high temperature applications(superalloys) such as jet engine components, rocket

parts, nuclear reactor parts, chemical plants, coins,

marine applications, solenoids

Nickel alloys exhibit high strength and corrosion


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resistance at elevated temperatures especially

when alloyed with Chromium, Molybdenum and

Cobalt. Examples: Monel alloy - Ni + Cu, used for

chemical applications, coins, pump shafts;

Inconel - Ni + Cr; very high UTS (1400

MN/m2); used in gas turbines, nuclear reactors;Hastelloy - Ni+Cr+Mo; high corrosion

resistance at elevated temperatures; gas

turbines; jet engines; Nichrome - Ni + Cr + Fe;high electrical resistance and resistance to

corrosion; used for electrical elements; Invar

alloys - Ni +Fe; Low thermal expansion

Superalloys


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Superalloys

Important in high temperature applications;

HEAT RESISTANT or HIGHTEMPERATURE alloys

High corrosion resistance, high UTS and

fatigue strength at elevated temperatures,good thermal shock resistance

Most have a service temperature up to

1000oC General applications - jet engines, rocket

engines, dies for metal working, chemical

plants, tools, nuclear reactors

A) Iron-base superalloys:


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A) Iron base superalloys:

generally contain 32 - 67% Fe + Cr, Ni.

Example - IncoloyB) Cobalt-base superalloys:

35 - 65% Co + Cr, Ni. Not as strong as Ni

baseC) Nickel-base superalloy:

Most widely used. Contains 38 - 76% Ni +

Cr, Mo, Co, Fe (See Ni and alloys)

Titanium and Alloys


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Titanium and Alloys Expensive. High specific strength, high

corrosion resistance even at elevated

temperatures. Properties very sensitive to

alloying elements

General applications - aircraft parts, jet

engines, racing cars, chemical, marine,

submarine components, biomaterials

(bone implants)

Major alloying elements in decreasingorder: Aluminum, Vanadium, Molybdenum,

Manganese

Refractory Metals and Alloys


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Refractory Metals and Alloys

Principal property is very high melting point

Molybdenum : Very high melting point.

Main alloying elements: Ti and Zr

Applications - solid-propellant rockets, jet engines,

honeycomb structures, heating elements, dies

Niobium:

Good ductility and formability, good resistance to

oxidation

Applications - rockets and missiles, nuclear and

chemical plants, superconductors

Tungsten:


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Tungsten:

Highest melting point (3410oC), high strength at

elevated temperatures, high density, low resistance

to oxidationApplications - Welding electrodes, spark plugs,

dies, circuit breakers, throat liners in missiles, jet

engines

Tantalum:

High melting point, good ductility, oxidation

resistant, high resistance to corrosion at low

temperaturesApplications - electrolytic capacitors, acid-resistant

heat exchangers, diffusion barriers

(microelectronics)

Beryllium


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Beryllium

High specific strength. Toxic if inhaled, dust from

machining etc.

Pure Beryllium used in rocket nozzles, space and

missile structures, aircraft disc brakes

Widely used as an alloying element e.g with Cu -

springs, non sparking toolsZirconium

Good strength, ductility and corrosion resistance at

elevated temperatures Used in electronic components, nuclear reactor

parts. Widely used as an alloying element

L M lti P i t All


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Low Melting Point Alloys

Lead: High density, good resistance to corrosion, soft. Fairlytoxic. Good vibration damping.

Applications - radiation shielding, vibration and sound

damping, weights, ammunition, chemical plants Alloying with Antimony and Tin enhances properties

and makes it suitable for production of collapsible

tubes, bearing alloys, lead-acid storage batteries

Extensive applications in solders when alloyed with tin Toxicity is causing it to be largely removed from

consumer electronics solders

Zinc:


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4th most widely used metal.

Used for galvanized iron sheets

Main alloying base for die-casting alloys - fuel pumps and grills for

cars, household components

Major alloying elements: Al, Cu and Mg

Also suitable for superplastic applications

Tin:

Main application of pure tin is in coating of steel sheets for food cans. Tin-base alloys - WHITE METAL - contain copper, antimony and lead

- used for journal bearings (Babbit metal)

Tin is an important alloying element for dental alloys, for bronze and

for solders (with lead)

Low melting point (232 C) makes it suitable for float glass process

Precious Metals


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Precious Metals

Gold - ductile, good corrosion resistance.

Applications: jewelry, ornaments, electroplating,coinage

Silver: ductile, highest electrical conductivity.

Applications : jewelry, coinage, electroplating,electrical applications, photographic film, solders

Platinum: ductile, good corrosion resistance.

Applications: electrical contacts, spark-plug

electrodes, catalysts, jewelry, dental applications,thermocouples

Others


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Others

Shape Memory alloys:

When deformed plastically at room temperature will

return to original shape upon application of heat.

Example 55%Ni/45%Ti.

Applications - antiscald valves in hot water systems,eye glass frames, connectors

Amorphous alloys

Are not crystalline, made by rapid solidification. High

strength, low loss from magnetic hysteresis. Cores

for transformers, generators.

Nanomaterials


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Nanomaterials

Materials having sizes in the order of 1 -

100 nm. Currently under very active research

Microelectromechanical devices, medical

applications


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Ceramics, Glass, Graphite,

Composite Materials


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Ceramics, Glass, Composite

Materials

76

Ceramics

Compounds of metals and non-metals traditional - bricks, clay, tiles

engineered - made for specified applications

such as automotive, aircraft, e.t.c.Structure

Bonding normally covalent or ionic

usually high hardness, thermal, andelectrical resistance.


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Mechanical Properties

Aluminum oxide strength in compression2100 MPa, flexural strength 500 Mpa

Ceramics are much stronger in

compression than in tension, why?

Stress concentration, by grains, defects,

design.

High strength requires small grain size

Creates opportunities for composites for

some applications


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Cermets - combinations of a ceramic phase bonded with


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Materials

79

p

metal. (composite!)

High temperature applications: tools, jet engine nozzles, aircraft

brakes

Silica: -polymorphic material abundant in nature. Bricks,

glasses, quartz. SiO2 hard - tool materials.

Nanophase ceramics and composites: ductility improve

by reducing particulate size (e.g. by gas condensation)

important parameters: particulate size, distribution and

contamination

Better ductility than conventional ceramics, easier to fabricate.

Used for auto and jet engine components (e.g. valves, rocker

arms, cylinder liners)

General properties


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Materials

80

p p

generally brittle, hard and strong, especially at high temperatures.

Maintain their strength and stiffness at high temperatures

low toughness, low thermal expansion low electrical conductivity

high wear resistance

thermal conductivity varies

in general, have lower specific gravity than metals but higher

melting points and higher elastic moduli

Phase transitions, ion conduction, and symmetry, can be important

for applications

Properties are the result of chemistry and structure (what makes

something piezoelectric, ferroelectric, insulating, etc.?)

Applications


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Materials

81

pp

electrical and electronic industry insulators, capacitors

sanitary ware (e.g. porcelain)

high temperature applications (cylinder liners, bushings,seals, bearings)

coating on metals - to reduce wear, prevent corrosion,

thermal barrier (e.g titanium nitride coating on tungsten

carbide tool inserts; tiles in space shuttle to providethermal barrier on re-entry/exit to atmosphere)

low density and high stiffness - ceramic turbochargers

strength and inertness - bioceramics (e.g. bone

implants) aluminum oxide, silicon nitride Microelectronics insulators, diffusion barriers, gate

dielectrics, capacitors, sensors

Symmetry and Crystallography are


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important for many of the electronic

applications of ceramics

Perovskite structure,

symmetric no net

electric field

Distorted structurenet electric field

* http://vpd.ms.northwestern.edu/members/Zixiao/Perovskite.jpg

BaTiO3, PbTiO3, etc.

exhibit this behavior

Glass


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Materials

83

Glass amorphous solid, supercooled at a rate so high that

crystals do not form

has no distinct melting/freezing point - glass transition

temperature, Tg

contains at least 50% silica (glass former); composition

generally resistant to chemical attack; have special

significant applications in optics (CRTs, LCDs, TVs,

lighting, containers, cookware, microelectronics

especially chalcogenide glasses)

St t f Gl


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Structure of Glass

SiO44-

tetrahedralbuilding blocks

give short range

order, but there is

no long range

order.

* http://www.ohsu.edu/research/sbh/results.html

Modifiers can also

change the structure

properties of the glass (but not strength) can be modified


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Materials

85

by adding various types of oxidesMODIFIERS

what does modify the strength?

Properties of glasses: - elastic but brittle, high strength,low thermal conductivity and expansion, high electrical

resistance

glass ceramics starts as a glass, but is partially

crystallized by heat treatment (usually 70+%crystallized). The crystalline component has a negative

coefficient of thermal expansion, the glass has a positive

CTE excellent thermal shock resistance

Gl M difi


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Glass Modifiers

Na lowers meltingpoint, but increases

water solubility

Ca improves water

resistance

B thermal properties

Pb refractive index Fe color (brown)

Co color (deep blue)

Ce UV absorption

P diffusion barrier for

sodium

(microelectronics)

Modifiers can alter properties to suit different

applications.

T il f il i l


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Tensile failure in glass

O

O

SiSi

O

SiSi

HHH2O

Si

O

Si

O O

Scratches intensify stresses reduces strength

Water attacks Si-O-Si bonds reduces strength

Flame polishing removes scratches increases strengthHF polishing removes scratches increases strength

Like other ceramics glass is much stronger in compression than in tension

Unlike other ceramics glass lends itself to tempering

Graphite


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Materials

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Crystalline form of carbon

lower frictional properties - used as SOLID LUBRICANT e.g.

in metal forming brittle; strength and stiffness vary with temperature

Amorphous C is used as a pigment (black soot) and rubber

additive (carbon black)

high electrical and thermal conductivity, good resistance to

thermal shock at high temperatures - used in electrodes,

heating elements, motor brushes, furnace parts

low resistance to chemical attack - filters for corrosive fluids

graphite fibers - used to reinforce composites

Diamond


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Materials

89

2nd principal form of carbon

Hardest substance known, brittle - used for tool

materials, polishing, grinding, etc.

polycrystalline diamond ornaments and abrasives

synthetic diamond - can also be made into particles

- used in abrasive cutting wheels other uses - dies for very small diameter wire

drawing; coatings for cutting tools and dies

Diamond Like Carbon (DLC) can be produced as

a thin film for wear resistance hard disks

C it M t i l


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Materials

90

Composite Materials

A major development and one of the mostimportant classes of engineering materials.

These materials are referred to as

ENGINEERED MATERIALS (c.f. Natural

composites - wood.)

Composites consist of the MATRIX - base

material and the REINFORCING material

usually fibers Widely used in aerospace and structures

Reinforced Plastics


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Materials

91

Matrix is a polymer or plastic

Reinforcement consists of various types of fibers

such as glass, graphite, boron, or aramids

Fibers are strong and stiff in tension but brittle, and

can degrade. Property depends material and

method of processing Matrix - tough

Reinforced plastic will contain the advantage of the

two

% of fibers by volume in the composite for reinforced

plastics varies between 10 and 60

Reinforcing fibers: -

Glass most widely used and least expensive (Glass fiber


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Materials

92

Glass - most widely used and least expensive. (Glass fiber

reinforced plastics - GFRP) glass should be weak in tension, why

does this work?

Graphite - more expensive than glass but low density, high strengthand stiffness (Carbon fiber reinforced plastics -CFRP)

Conductive graphite - are a recent development to enhance the

electrical and thermal conductivity of CFRP. Fibers coated with metal.

Used in electromagnetic and radio frequency shielding, and lighting

protection Aramids - among the toughest fibers. E.g. KEVLAR. But hygroscopic,

complicates their use

Boron - fibers deposited by chemical vapor deposition onto tungsten

fibers. High strength and stiffness, resistance to high temperatures.

Heavy and expensive Others - nylon, silicon carbide, aluminum oxide, steel; whiskers

Fibers can be short or long, continuos or discontinuous

Matrix materials:


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Materials

93

have three functions:-

support fibers in place and transfer the stresses to them

while they carry the most load protect fibers against physical damage or environment

reduce propagation of cracks in the composites - ductile

Are usually thermoplastics or thermosets

Properties

mechanical and physical properties depend on the kind,

shape and orientation of fiber

long fibers offer more effective reinforcement bonding between matrix and fiber is very critical - weak

bonds give rise to delaminations, and fiber pullouts

especially under adverse environmental conditions

Highest stiffness obtained when fibers are aligned in the direction of

tensile load


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Materials

94

tensile load

Fiber can be re-arranged in reinforced composites to give the part a

specific service condition. For instance if the part is subjected to

forces in different directions, either the fibers can be crisscrossed indifferent directions or the layers of fibers can be built up into

laminate having improved properties in more than one direction

Applications

Formica (table tops).

Reinforced plastics typically used in military and commercial aircraft

(B777 - 9% composites), rocket components, helicopter rotor

blades, automobiles (e.g. bumpers), leaf springs, drive shafts,

pipes, tanks, pressure vessels, boats

Metal Matrix composites


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Materials

95

higher stiffness than polymer matrix composites

posses better properties at higher temperatures than

polymer matrix composites BUT higher density and difficulty in processing

matrix materials - aluminum, magnesium, aluminum-

lithium, copper, titanium, and superalloys

fiber materials - graphite, aluminum oxide siliconcarbide, boron molybdenum and tungsten

boron fibers in aluminum - space shuttle structural

beams ( high specific stiffness and strength, high

thermal conductivity) hypersonic aircraft (under development)

Ceramic-matrix composites


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Materials

96

matrix is ceramic

have high temperature resistance and resistance to

corrosive environments

matrix materials - silicon carbide, silicon nitride,

aluminum oxide, carbon

fibers - carbon, aluminum oxide applications - jet and automotive engines, deep sea

mining, cutting tools, dies.

Reinforced concrete very widespread use, steel

has a corrosion problem, why does this work?


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Polymers: Structure and

Properties


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Polymers - Structure, Properties

and Applications

98

Why Polymers?

Easily formed into shape with less energy andfewer finishing operations

Low density

High corrosion resistance

Low electrical and thermal conductivity

Cheaper than metals and ceramics

But some limitations:- low strength/stiffness, low

service temperature, some polymers degradewith time in sunlight

Formation of Polymers


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and Applications

99

Short hydrocarbon chains monomersform into long chains - Polymerization

Synthesis of polymers can be initiated by: Heat or catalyst addition polymerization

monomers reacting together when mixedcondensation polymerization. By products such as

water are condensed out. Polymer chains formed can be:

linear

branched

cross linked networked

In most cases the structure is amorphous


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and Applications

100

palthough some crystallization may occur

Both of these affect the density andproperties

The degree to which they occur (degree ofcrystallinity) can be controlled in thepolymerization process

The degree of crystallinity affects themechanical and physical properties:

higher crystallinity implies higher density, higherstiffness, less ductile, more resistant to solvents and

temperature

Molecular weight (MW) - sum of the


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and Applications

101

Molecular weight (MW) sum of themolecular weights of the mers in a

representative chain. The higher theMW the greater the average chainlength. (i.e chain lengths vary) MW has a strong influence on the properties -

tensile strength, toughness and viscosity increasewith chain length. Typical values ~104 to 107

Degree of Polymerization - ratio of the MW ofpolymer to the MW of the mer.

Example PVC: MW of mer = 62.5 DP of PVC with MW of 50,000 = 50,000/62.5= 800

Example: formation of polyethylene form


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and Applications

102

Example: formation of polyethylene form

ethylene

Glass Transition Temperature


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and Applications

103

Amorphous polymers do not have a

specific melting point but undergo adistinct change in behavior over a

specific temperature range

This is known as the glass transitiontemperature, Tg

Below Tg hard, rigid and brittle

Above Tg rubbery and leathery Tg important in service considerations

and production

Additives

T i h t i ti b l T l


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and Applications

104

To improve characteristics below Tg polymers canbe blended.

Several types:Fillers solid or fibrous, improve mechanical

performance

Plasticizers e.g. elastomer, lowers Tg

andimproves toughness

Colorants dies and pigments, impart requiredcolor; carbon provides protection against UVradiation

Others flame retardants, lubricants (reducefriction during forming process), cross-linkingagents

Types

Th b i t f l


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and Applications

105

Three basic types of polymers:

Thermoplastics Polymers which can be raised to

temps above their Tg and cooled (softened andhardened) without modifying any of their originalmaterial propertieseffects of heating arereversible

Examples: Nylons, Fluorocarbons (Teflon), PVC,Polystyrenes

If temp of thermoplastic is raised above Tg,becomes a viscous fluid (not definite melting

temperature, softens over range of temp)Repeated heating and cooling cycles producesthermal degradation (thermal aging)

Teflon


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Teflon

Poly(tetrafluoroethene)

Very non-reactive non-stick coatings for cookware, hardened munitions,

etc.Discovered accidentally during refrigerant research

Tends to creep at room temperature can be both good and bad depending

on design

PVC


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PVC

Polyvinyl chloride (polychloroethene)

Huge number of uses plumbing, magnetic stripe cards, hoses, flooring,

electrical insulation (fire retardant)

Plasticizers enabled use and processing

Can be further chlorinated with chlorine gas and UV to replace some of thehydrogen (CPVC) increases TG

Thermosetting polymers -The polymerization bondsi th t i l t d t th


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and Applications

108

in these materials are set and permanentthus,the curing reactions are irreversible (unlike

thermoplastics); "non-recyclable" material, cannotbe melted (will decompose first)

Examples: Epoxies, Silicones, Polyesters,Urethane (some are thermoplastic)

No well defined glass transition temptwo stagecuring process:(1)mix molecules to partially polymerize into linear chains

and

(2) set molecular structure by heating, forming and coolingprocesses

Better mechanical properties in general thanthermoplastics

Silicones


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Silicones

Contain silicon, carbon, hydrogen, andoxygen, and sometimes others.

polydimethyle siloxane

Good temperature stability, chemical

resistance, electrically insulating, non-toxic, somewhat gas permeable

Polyurethane


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Polyurethane

Depending on R groups useful for

foams, insulation, adhesives, tires,furniture, sealants, coatings.

Epoxies


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po es


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Epoxies


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p

Three dimensional cross linked polymers Usually applied in two parts

Useful for coatings and as matrix for

composites. Properties can be tailored by adjusting R

groups.

Elastomers Exhibit large elastic deformations, low

T ft h h t i l ff t d i


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and Applications

114

Tg, soft, show hysteresis loss effects during

unloading - differences in curves represents

energy loss (vibration dampening and soundabsorbing)

Elastomers can be "thermoset" by vulcanization

and cross-linking of polymer chains occurs at hightemperatures can also be thermoplastics

Examples: tires; hoses; tennis shoe soles; tooling

(esp. urethanes)


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Lecture 01 Manufacturing

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