Phase Any physically distinct, chemically homogeneous and mechanically separable portion of a...

PhasePhase• Any physically distinct, Any physically distinct,

chemically homogeneous chemically homogeneous and mechanically separable and mechanically separable portion of a substanceportion of a substance

• Can be continuous or Can be continuous or discontinuousdiscontinuous

• Can be solid, liquid or gasCan be solid, liquid or gas• Can be a pure substance or Can be a pure substance or

a solutiona solution

Multiple Solid Phases

• Multiple solid phases are Multiple solid phases are common in metalscommon in metals

• Phases defined by Phases defined by composition (not by composition (not by state – solid, liquid, gas)state – solid, liquid, gas)

• Example – two phases Example – two phases shown to the right, dark shown to the right, dark phase and then the phase and then the lighter phaselighter phase

Single Phase vs. Multiple PhasesSingle Phase vs. Multiple Phases

SolubilitySolubility

• Unlimited SolubilityUnlimited Solubility– Hume Rothery’s Hume Rothery’s

Conditions Conditions • Similar SizeSimilar Size• Same Crystal StructureSame Crystal Structure• Same ValanceSame Valance• Similar ElectronegativitySimilar Electronegativity

– Implies single phaseImplies single phase

• Limited SolubilityLimited Solubility– Implies multiple phasesImplies multiple phases

• No Solubility (oil and No Solubility (oil and water region)water region)

Solid Solutions

• Just like we have liquid solutions (ex mixing alcohol and water => liquid solution), we can have solid solutions.

• Solid solution is mixed as a liquid and then allowed to solidify – May mix two metal elements together then

allow to solidify => solid solution

Two Types of Solid SolutionsTwo Types of Solid SolutionsInterstitial Solid SolutionInterstitial Solid Solution Substitutional Solid SolutionSubstitutional Solid Solution

Equilibrium Phase DiagramEquilibrium Phase DiagramCooling CurveCooling Curve

Tem

pera

ture

Time

LocalSolidification

Time

TotalSolidification

Time

Thermal Arrest

Superheat

T/t

REMEMBER THIS?

Cooling Curves and the Phase DiagramCooling Curves and the Phase Diagram

In your groups, work on problem 10-57 in your book

You just made a phase diagram!

Comp.(wt % V)

temp ( C )

0 262520 250020 230040 235040 215060 222560 205080 210080 1975

100 1910

Equilibrium Phase DiagramEquilibrium Phase Diagram• Equilibrium: state of a system remains constant over an indefinite period of Equilibrium: state of a system remains constant over an indefinite period of

timetime

• Binary phase diagram: diagram for alloy composed of two elementsBinary phase diagram: diagram for alloy composed of two elements

• Shows relationship in a metal among Shows relationship in a metal among – temperaturetemperature

– pressurepressure

– compositioncomposition

• Gibb’s Phase RuleGibb’s Phase Rule

Types of Phase diagramsNumber of Constituents

• Unary (like the water one shown at the beginning) – one constituent

• Binary - two constituents , like an alloy (we will focus on these)

• Ternary - three constituents; requires 3-D diagram

Number of phases

• Isomorphous – one solid phase

• Polymorphous – multiple solid phases

Utilization of Phase DiagramsUtilization of Phase Diagrams• For each point of temperature and composition, three pieces of For each point of temperature and composition, three pieces of

information can be obtainedinformation can be obtained– Phase present Phase present

– The amount of each phase present ( how many ice cubes are in the glass)The amount of each phase present ( how many ice cubes are in the glass)• lever lawlever law

– Composition of each phase (chem make-up of phases)Composition of each phase (chem make-up of phases)• tie linetie line

Liquidus and Solidus Temperature

• Liquidus – The temperature at which the first solid forms during solidification

• Solidus – The temperature below which the liquid has completely solidified.

liquidus

solid

us

Wt % MgO

Tie Line –Composition of Phases

• Draw a vertical line at the composition of the “alloy” of interest ex – 40 wt % MgO see purple line

• For a given temperature draw an isotherm (horizontal line) ex at 2400 C red line

• Where line crosses “phase boundary” (in this case the liquidus line or solidus line), draw a vertical line– Ex – composition of liquid

phase is ~32% MgO; Composition of solid phase is ~ 60 % MgO

liquidus

solid

us

Wt % MgO

Lever Law – Amount of each phaseUsing the compositions of the phases determined from the tie line, calculate the amount of each phase as this:

Opposite lever arm/total length of lever * 100%

LiquidC = 32 %MgO

SolidC = 60 %MgO

AlloyC = 40 %MgO

Therefore:Amt L = (60-40)/(60-32) * 100 = 71%Amt S = (40-32)/(60-32)*100 = 29%

**Notice the compositionof the phases does not have to add up to

100% but the amount does!!*****

What’s the difference between Amount and Composition????

• Composition is the chemical make-up of the phase (if we had a glass of coke with ice in it, our liquid phase would have one chemical make-up – won’t begin to think what it might be, the liquid phase would have a chemical make-up of ~ H2O. The composition of the “alloy” would be the total chemical make-up of the ice and coke combined (which would be watery coke?)

What’s the difference between Amount and Composition????

• Amount is the quantity of the phase (if we had a glass of coke with ice in it, we could take the ice cubes out and weigh them and then weigh the coke to figure out the amount of the solid and liquid phase or use the lever law)

http://michellegeller.typepad.com/michelle_geller_weblog/images/2007/03/28/gluttony.jpg

Phase Diagram and MicrostructurePhase Diagram and Microstructure

• Can you relate this to nucleation and growth?• Where does

nucleation occur?• Where does growth

occur?

Solidification of Alloy, xSolidification of Alloy, x

Three-Phase Three-Phase ReactionsReactions

• Involves 3 distinct phases• Occurs at a single “point”• Often times is associated

with special properties or characteristics for that material

• Eutectic L => S1 + S2• Eutectoid S1 => S2+ S3• Peritectic L + S1 => S2• Peritectoid S1 + S2 => S3• Monotectic L1 => S1 + L2• Miscibility gap; Oil and

water region, where two liquid phases coexist

Intermetallic

• A compound formed of two or more metals that has its own unique composition, structure and properties.

• Exists as a single phase region where you would expect a two phase region

• Typically hard, brittle and strong• Stoichiometric – single composition• Non Stoichiometric – range of compositions

Solvus

• Indicates solubility limit

Group WorkID all of the three phase reactions by name and “reaction”

Hypo- and Hyper-EutecticHypo- and Hyper-Eutectic

Hyper-Eutectic vs. Hypo-Eutectic Hyper-Eutectic vs. Hypo-Eutectic Microstructural DifferencesMicrostructural Differences

Composition and theComposition and theMicrostructure of Lead TinMicrostructure of Lead Tin

Lead-Tin Eutectic MicrostructureLead-Tin Eutectic MicrostructureT

e mpe

r at u

r e

Iron- Carbon Equilibrium DiagramIron- Carbon Equilibrium Diagram

PhasesPhases

- delta ferrite- delta ferrite

- austenite- austenite

- alpha ferrite (ferrite)- alpha ferrite (ferrite)

FeFe33C - cementiteC - cementite

ReactionsReactions

Peritectic (L+ SPeritectic (L+ S11 > S > S22))

Eutectic ( L > SEutectic ( L > S11 + S + S22))

Eutectoid (SEutectoid (S11 > S > S22 + S + S33))

Steels and the Simplified Iron- Carbon DiagramSteels and the Simplified Iron- Carbon Diagram

Ternary Phase DiagramTernary Phase Diagram