L2 Engineering Materials

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MEL120: Manufacturing Practices 1

Engineering Materials

Lecture 2


Selection of Material

A particular material is selected is on the basis offollowing considerations

1. Properties of material1. Properties of materialz Mechanical properties - strength, ductility,

toughness, hardness, strength to weight ratio etc.z Physical properties - density, specific heat, thermal

expansion, conductivity , melting point etc.

z Chemical properties - oxidation , corrosion,flammability, toxicity etc.

z Manufacturing properties - formed, casting,machined, welding


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Selection of Material

2. Cost of material

3. Availabili ty of material (desired shape and

size and quantity) & reliability of supply.

4. Service in l ife of material

z Dimensional stability of material wear , corrosion etc.,shorten life

5. Appearance of material5. Appearance of material

z Colorz Surface texture etc.


Manufacturing Materials

zz MetalsMetalsz Ferrous

z Pure iron is rarely used as an engineering material

z It is used in the form of alloys; composed of two or moreelements

z Generally these are classified on the basis of %C with Fe

z %C >2.11: Cast IronCast Iron; %C


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Cast Iron

z Elements added to improve casting properties

z Carbon = 2.11 4%

z Silicon = 0.5 3%

z Manganese = 0.4 1%

z Types of C.I. based on form of carbon present

z Grey Cast Iron

z White Cast Iron

z Malleable Cast iron

z Ductile or Nodular Cast iron


Grey Cast Iron

z Most commonly used

z Carbon is present as Graphite flakesGraphite flakes distributed throughoutz When it is fractured, the exposed surface of metal has gray

appearancez This dispersion ofGraphite flakesGraphite flakes provides good internal

lubricating property hence excellent machinability andvibration damping characteristics.

z It has poor tensile strength and ductilityz

It posses good compressive strength, wear resistance andcorrosion resistancez Commonly used for machine bodies, engine blocks, pumps

and motor housings, etc.


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White Cast Iron

z Produced by rapid cooingrapid cooing of molten gray CI

z Carbon remains chemically combined in the form of ironcarbide (cementite)

z When fractured, it has white shining appearancewhite shining appearance

z It is hard, brittle and posses excellent wear resistance

z Used for applications requiring high wear resistancehigh wear resistance,e.g., railway brake shoes, grinding balls, crushing rollers,etc.


Malleable Cast Iron

z It is obtained by heat treatmentheat treatment of white CI and carbon ispresent in forms of clusters

z This structure promoted toughness and ductilitytoughness and ductility

z It is used in making small tools, pipe fittings, automobileparts, farm implements, etc.


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Ductile or Nodular Cast Iron

z This is obtained by adding Mg or Cesium (nodulizingagents) to molten Gray CI before pouring.

z In this the carbon is present in the form ofspheroidsspheroids

z It has good ductility, high strength, toughness, wearresistance and excellent casting properties.

z It is popular material for making intricate castingsintricate castings

Cast irons are often alloyedalloyed with various elements

and heat treatedheat treated to achieve special properties likehigh hardness, temperature resistant, corrosionhigh hardness, temperature resistant, corrosion

resistantresistant etc.


Steels

z Carbon : 0.02 - 2.11%

z Other Alloying Elements

zz MnMn, Cr, Ni, Mo, etc., Cr, Ni, Mo, etc.

zType of Steels

z Plain Carbon Steel

z

Alloy Steelz Stainless Steel

z Tool Steel


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Plain Carbon Steel

z The strength increases with increase in %C but ductilitydecreases.

zz Low carbon s teelsLow carbon steels

z Less than 0.2% C0.2% C

z Most common steel known as mild steel

z Plates, sheets, rods, machine components, nut and bolts

zz Medium carbon steelsMedium carbon steels

zz 0.2 to 0.5 % C0.2 to 0.5 % C

z Used where high strength is required like engine components

zz

High carbon s teelsHigh carbon steelszz 0.5 to 2.11% C0.5 to 2.11% C

z Even high strength applications like tools, blades, springs


Alloy Steel

z Additional alloying elements are added to improve theimprove themechanical propertiesmechanical properties of plain carbon steel

zz Commonly added elementsCommonly added elements

zz MnMn ::To improve strength and hardness

zz Cr :Cr :To improve strength and wear resistance and hothardness

zz Cu :Cu :To improve strength and corrosion resistancezz Mo :Mo :To improve heat resistance and toughness

zz Ni :Ni :To improve strength and toughness

zz SiSi ::To improve strength and toughness


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Alloy Steel

z Total percentage of alloying elements 12%

z Other alloying elements include Ni, Mo, Ti, Si, Mn etc.

z Typical applications of these steel are for kitchen, surgical,chemical and food processing equipments.


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Tool Steel

z Highly alloyed steels designed for use as tools and diestools and diesin machining and forming process

z They are designed to provide high strength andtoughness and wear resistancewear resistance at both room andelevated temperatures

z In these materials wear resistance and toughness are

balanced by various combination of alloying elementsvarious combination of alloying elements


Tool Steel

z Tungsten (W) 1.5 - 20%

z Chromium (Cr) 0.2 -15%

z Molybdenum (Mo) 0.8 -15%

z Cobalt (Co) 0.75 -12%

z Vanadium (V) 0.15 - 3%

z Silicon (Si) 0.5 - 2%

z Manganese(Mn) 0.2 - 1.6%

z A variety of tool steels like high speed steelhigh speed steel, mouldmouldsteelssteels, hot-work tool steels, cold-work tool steels etc. areobtained.


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Non Ferrous Metals

z Not iron based

z Wide variety of materials such as Al, Cu,Al, Cu, MnMn, W,, W,

Tantalum and MoTantalum and Mo.

z Important because resistance to corrosionresistance to corrosion, highhigh

strength to weight ratiostrength to weight ratio, high electric and thermalhigh electric and thermal

conductivityconductivity


Aluminium & Alloy

z Extensively used for aircraft, bus, car andmarine craft bodies, cooking utensils etc.

z High strength to weight ratio resistance tocorrosion, good electrical and thermalconductivity


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Copper and Al loys

z Good conduction of heat and electricity

zz BrassBrass (65%Cu and 35% Zn), highconductivity, adequate strength and ductility

zz BronzeBronze (90%Cu and 10%tin), Good strength,toughness, wear strength and corrosionresistance


Magnesium and Alloys

z Lightest engineering Material with specificgravity as 1.751.75

zz Mg alloyMg alloy is used for various high-strength toweight ratio applications

zz Applications:Applications: Aircraft & missile components,material handling equipments, sporting goodsand general light weight components


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Nickel and Alloys

z Silver white metal. Used for electroplatingelectroplating forappearance and for improving corrosion resistance.

z Ni alloys offer high strength and corrosion resistanceat elevated temperature

zz MonelMonel a Ni- Cu alloy is used extensively in chemicaland food processing industries due to corrosionresistance property.

z Super alloys of Ni are used for high temperature

applications such as for jet engines, gas turbines,and rocket components and in nuclear power plants.


Zinc

z A low melting point metal

z Main use in galvanizing on iron and steel forproviding corrosion resistance

z Zinc alloys are primarily used for die castingof components for automobile and applianceindustries


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Titanium

z High strength to weight ratio and corrosionresistant material at elevated temperature

zTi- alloys with alloying elements such as Al,Va, Mo, Mn etc. can be used up to 550c

z Attractive material for aerospace applications,marine, chemical and photo chemicalequipments


Ceramics

z Compounds of metallic and non-metallic elements.z Available in the form of oxides, carbide and nitridesz Brittle, have high strength and hardness at elevated

temperature, low thermal and electrical conductivityz Clay, Alumina, Quartz, SiC ,WC, Silicon Nitride,

CBN etc, are typical examplesz SiC : Abrasivesz CBN,WC: Popular cutting tool materialz Silicon Nitride: Application in gas turbines and rocket

enginesz Glass is also ceramic and inorganic non-metallic

compound


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Polymers

z Compounds of long chain molecules with eachmolecule made up of repeating units connectedtogether. They are organic compound

z Low density, strength, thermal & electricalconductivity, good chemical resistancegood chemical resistance

z Low working range of temperature


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Composite Materials

z Laminar or layer composites:

z Plywood, coated tools, insulated wires

z Particulate composite:

z Concrete (cement sand and gravel)

z Abrasive particles and matrix in grinding wheels

z Cemented carbides- particle of WC uniformlydistributed used as a cutting tool

z Properties are uniform in all direction


Composite Materials

z Fiber reinforced composite:

z Thin fibers of one material are embedded inmatrix of another material

z Glass is most widely used fiber with polymer asmatrix. Other fibers are carbon, boron etc.

z Properties depend upon the fibred material

volume fraction of fiber, orientation of fiber,properties of matrix, degree of bonding betweenfiber & matrix etc.


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Composite Materials

z Fiber Reinforced Composite:

z Polymeric materials are used for low temperatureapplications (below 300C), While MMC are usedfor high temperature application

z Steel reinforced concrete used in construction

z Nylon reinforced tires, glass fiber reinforcedplastics for car bodies

z Boron-reinforced components for aircraft & rocket

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