Introduction to ManufacturingIntroduction to Manufacturing

Metal Alloys (l.u. 2/15/10)Metal Alloys (l.u. 2/15/10)

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IntroductionIntroduction

The properties and behavior of metals (and alloys) The properties and behavior of metals (and alloys) depend on their:depend on their:

StructureStructure

Processing historyProcessing history

andand

CompositionComposition

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Structure of AlloysStructure of Alloys

An alloy is the An alloy is the combinationcombination of two or more chemical elements, of two or more chemical elements, oneone being a metal.being a metal.

Classification of alloys.Classification of alloys.

FerrousFerrous: containing iron, second most abundant element (5% : containing iron, second most abundant element (5% earth's crust).earth's crust).

Non-ferrousNon-ferrous: no iron, usually more expensive than ferrous : no iron, usually more expensive than ferrous metals.metals.

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(Black & Kohser, 2008, p. 125)

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SoluteSolute- - minorminor element (added to solvent) element (added to solvent)

SolventSolvent- - majormajor element (host) element (host)

Solid solutionSolid solution- structure of the solvent is maintained (one alloying element is - structure of the solvent is maintained (one alloying element is

completely dissolved in another)completely dissolved in another)

PhasePhase- liquid, solid, gas – pure substance or solution (uniformity)- liquid, solid, gas – pure substance or solution (uniformity)

Some elements have Some elements have limited solubility limited solubility – results in – results in mechanical mixture mechanical mixture (clear (clear

boundaries)boundaries)

Structure of Alloys (Cont.)Structure of Alloys (Cont.)

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1. Substitutional Solid Solutions1. Substitutional Solid Solutions

Substitutional Solid Solution (according to Hume-Rothery rules):Substitutional Solid Solution (according to Hume-Rothery rules):

Must have similar crystal structures (e.g. FCC with FCC).Must have similar crystal structures (e.g. FCC with FCC).

Difference between atomic radii less than 15% (same size Difference between atomic radii less than 15% (same size atoms).atoms).

Brass (zinc + copper).Brass (zinc + copper).

Copper Grains

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2. Interstitial Solid Solutions2. Interstitial Solid Solutions

Interstitial Solid Solution - solvent atom has more than one Interstitial Solid Solution - solvent atom has more than one valence electron (easier to control solute).valence electron (easier to control solute).

Atomic radius of solute atom is less than 59% of solvent (atom Atomic radius of solute atom is less than 59% of solvent (atom sizes differ greatly).sizes differ greatly).

Example = Steel (iron + carbon)Example = Steel (iron + carbon)

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Intermetallic CompoundsIntermetallic Compounds

Complex structuresComplex structures

Solute atoms present among solvent atoms = atomic bonding.Solute atoms present among solvent atoms = atomic bonding.

Strong, hard, and brittleStrong, hard, and brittle

TiTi33Al, NiAl, Ni33Al, FeAl, Fe33Al.Al.

Aluminum Grains

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Two-phase SystemsTwo-phase Systems

Most alloys Most alloys consist of consist of twotwo or more solid phases (alloy contains or more solid phases (alloy contains particles of single element particles of single element OROR grains are differentgrains are different).).

Limited solubility (just as with sugar in water Limited solubility (just as with sugar in water Mechanical Mechanical

mixture).mixture).

Clear boundaries, mixture - each with its own properties.Clear boundaries, mixture - each with its own properties.

Stronger and less ductile than solid solutions.Stronger and less ductile than solid solutions.

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Phase DiagramsPhase Diagrams

Pure metals have clearly defined melting or freezing points, and Pure metals have clearly defined melting or freezing points, and

solidification takes place at a constant temperature.solidification takes place at a constant temperature.

Tool for understanding the relationship among Tool for understanding the relationship among temperaturetemperature, ,

compositioncomposition, and , and phasesphases present in a particular alloy system. present in a particular alloy system.

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Phase Diagrams (Cont.)Phase Diagrams (Cont.)

Alloys solidify over a Alloys solidify over a range of temperaturesrange of temperatures, based on the , based on the

composition of the mixture.composition of the mixture.

As the alloy cools the mixture begins to freeze, changing gradually As the alloy cools the mixture begins to freeze, changing gradually to a solid (liquid/solid phases).to a solid (liquid/solid phases).

Time

Tem

per

atur

e

L SL+S

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Binary Phase DiagramsBinary Phase Diagrams

Composition

Tem

per

atur

eL

S

L+S

Tem

per

atur

e

0% B100% A

100% B0% A

A

B

Complete Solid Solubility

Solid Solution - Single Phase

Two Phases

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Nickel-Copper DiagramNickel-Copper Diagram

(Black & Kohser, 2008, p. 75)

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A + Liquid

B + Liquid

A + B

A

B

0% B100% A

Eutectic point

100% B0% A

AB

Two-Phase DiagramsTwo-Phase Diagrams

Limited solubilityLimited solubilityTwo Phases

Solid Solution - Single Phase

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Two-Phase Lead-Tin DiagramTwo-Phase Lead-Tin Diagram

(Black & Kohser, 2008, p. 75)

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Two-Phase Lead-Tin DiagramTwo-Phase Lead-Tin Diagram1) At the point of maximum solubility, 183 C, lead can hold up to 1) At the point of maximum solubility, 183 C, lead can hold up to 19.2% tin (and be in single phase solution) 19.2% tin (and be in single phase solution)

2) Tin can hold up to 2.5% lead in single phase (@ 183 degrees C).2) Tin can hold up to 2.5% lead in single phase (@ 183 degrees C).

3) 61.9% tin added to lead provides the lowest melting temperature 3) 61.9% tin added to lead provides the lowest melting temperature (eutectic point)(eutectic point)

(Black & Kohser, 2008, p. 75)

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Two-Phase Iron-Carbon DiagramTwo-Phase Iron-Carbon DiagramMost important phase diagram in manufacturing applications, since Most important phase diagram in manufacturing applications, since steels, cast irons, and cast steels are the most common engineering steels, cast irons, and cast steels are the most common engineering materials (versatile properties and relative low cost).materials (versatile properties and relative low cost).

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Iron-Carbon Diagram (Cont.)Iron-Carbon Diagram (Cont.)

Solid Phases of the Iron-Carbon DiagramSolid Phases of the Iron-Carbon Diagram

Ferrite (Ferrite (-iron)-iron)

Austenite (Austenite (-iron)-iron)

Cementite (iron-carbide)Cementite (iron-carbide)

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FerriteFerrite

((-iron-iron))

Soft, ductile, magnetic.Soft, ductile, magnetic.

BCCBCC

Solid solution (0.022% carbon) almost pure iron.Solid solution (0.022% carbon) almost pure iron.

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AusteniteAustenite ((-iron)-iron)

FCC - higher density than BCC, ductile at elevated FCC - higher density than BCC, ductile at elevated temperatures (good formability)temperatures (good formability)

Interstitial Solid Interstitial Solid

Solution (2.11% carbon)Solution (2.11% carbon)

Non-magneticNon-magnetic

AUSTENITIC MANGANESE STEEL (www.ccipope.com.au)

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CementiteCementite

Iron carbide (Fe3C) 6.67% carbonIron carbide (Fe3C) 6.67% carbon

Hard & brittle Intermetallic Compound.Hard & brittle Intermetallic Compound.

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Heat Treatment of Ferrous AlloysHeat Treatment of Ferrous Alloys

The different The different microstructures of an alloy can be modifiedmicrostructures of an alloy can be modified by by controlled heating and cooling which will induce phase controlled heating and cooling which will induce phase transformations and thus, changes in mechanical properties.transformations and thus, changes in mechanical properties.

Heat treatment is one of the most Heat treatment is one of the most common methodscommon methods to improve or to improve or modify characteristics, since it can produce a variety of mechanical modify characteristics, since it can produce a variety of mechanical properties and improve service performance.properties and improve service performance.

The The effecteffect of thermal treatment of thermal treatment dependsdepends on the alloy, its on the alloy, its composition, microstructure, degree of prior cold work, and rates of composition, microstructure, degree of prior cold work, and rates of heating and cooling.heating and cooling.

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Steel MicrostructuresSteel Microstructures

Perlite (eutectoid steel) - alternating layers of Ferrite and CementitePerlite (eutectoid steel) - alternating layers of Ferrite and Cementite fine or coarse perlitefine or coarse perlite

  Spheroidite (spherical cementite) - tougher and harder than perliteSpheroidite (spherical cementite) - tougher and harder than perlite

Bainite (very fine ferrite-cementite) - stronger and more ductile than Bainite (very fine ferrite-cementite) - stronger and more ductile than perlite, same hardnessperlite, same hardness

Martensite (tetragonal body-centered structure) - austenite cooled at Martensite (tetragonal body-centered structure) - austenite cooled at high rate, hard and brittle (not practical)high rate, hard and brittle (not practical)

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Heat Treatment Heat Treatment ProcessesProcesses

AnnealingAnnealing: general term used to refer to the : general term used to refer to the restorationrestoration of of properties after cold work or heat treatment.properties after cold work or heat treatment.

NormalizingNormalizing: cooling cycle done in still : cooling cycle done in still airair to avoid excessive to avoid excessive softness in the annealing of steels. softness in the annealing of steels.

SpheroidizingSpheroidizing: improve properties of high-carbon steels.: improve properties of high-carbon steels.

Stress RelievingStress Relieving: reduce or eliminate residual stresses.: reduce or eliminate residual stresses.

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TemperingTempering: reduce brittleness and residual stress, and increase : reduce brittleness and residual stress, and increase ductility and toughness of previously hardened steels.ductility and toughness of previously hardened steels.

HardeningHardening: heating and cooling rapidly (quenching): heating and cooling rapidly (quenching)

Case HardeningCase Hardening: complete alteration of the microstructure and : complete alteration of the microstructure and properties of just the surface of the material by heating within a properties of just the surface of the material by heating within a particular atmosphere.particular atmosphere.

Heat Treatment Heat Treatment Processes (Cont.)Processes (Cont.)