Chapter Four: Phase Diagram and Microstructure ·Component Components are pure metals and/or compounds of which an alloy is composed. Ex: in copper-zinc brass, the components are Cu and Zn. ·System First, "system" may refer to a specific body of material under Consideration Or, it may relate to the series of possible alloys consisting of the same components, but without regard to alloy composition (e.g., the ironcarbon system)
• Component Components are pure metals and/or compounds of which an alloy is composed. Ex: in copper-zinc brass, the components are Cu and Zn. • System First, "system" may refer to a specific body of material under Consideration Or, it may relate to the series of possible alloys consisting of the same components, but without regard to alloy composition (e.g., the ironcarbon system). Chapter Four: Phase Diagram and Microstructure
Solubility LimitFormanyalloysystemsandatsomespecifictemperature,there is a maximum concentration of soluteatoms that may dissolveinthe solventto form asolidsolution.100200Solubilityslimitlimit80(do)(neaa150Liquidinee60SarutionLiguid'solution (syrup)solid+40100Soidsugar205010Sugar20406080100010080604020oWaderComposition(w%)
Solubility Limit For many alloy systems and at some specific temperature, there is a maximum concentration of solute atoms that may dissolve in the solvent to form a solid solution
Phasesphasesbedefinedasahomogeneousportionofasystemthathas uniformphysical and chemicalcharacteristicsPhasesDiagramPhases Diagram-a graphic representation showing thephaseorphasespresentforagivencompositionasafunction oftemperature15001400Led013001270°375032451250°120040α110011000406080Ni20CuWeightpercentnickel
Phases phases be defined as a homogeneous portion of a system that has uniform physical and chemical characteristics. Phases Diagram Phases Diagram - a graphic representation showing the phase or phases present for a given composition as a function of temperature
Binary alloy phase diagram15001455'Liquidus1400LTheequilibrium phase(0.)12801300Solidusdiagrams for the Cu2800L1240*Ni and NiO-MgO26001200at2400L+Ssystems.110010852200S(Ni, Mg)O10002000The liquidus and2040Cu6080NiNiO20406080MgOWeight percent nickelMole percent MgOsolidus temperatures(a)(b)1600are shownfor a Cu-LiquidLiquid40% Ni alloy.(0.)amexdmeSolidsolution+L4001500and Systems with-300Solid solutionSolid solution+Lsolid solution maxima1400Solid solution2040608020406080and minima.TIPbCaO·SiO2SrO·SiO2Weight percentWeight percent(c)(d)
AnalloyconsistsofXaat%of Awithanatomicweight aA,andXat%ofBwithanatomicweighaB.Derive an equation for the concentration of A in wt%.By symmetry,write down the equation for theconcentrationofBinwt%Consider 100 atoms: mass of A atoms = a AX A and mass of B atoms = aBXB .aAXAaBXBWA=aAXA+aBXBand by inspection, Ws = aAX A+agX B
ThePhaseRuleF=C-p+2F=#degrees of freedomThe number of intensive parameters that must be specifiedinordertocompletelydeterminethesystemp=#ofphasesphases aremechanically separableconstituentsC= minimum # of components (chemical constituents that mustbespecifiedinordertodefineallphases)2=2intensiveparametersUsually=temperature and pressure
The Phase Rule
EutecticsZTTLiquidusLiquidcurveXB + liquidA+liquiddCySoliduseA+BcurveABCompositionGibbs'phase rule:F=C-P+2orthecondensed rule ifthevaporpressureisnegligibleF=C-P+1.F: # degrees of freedom (independent variables) among T, p, compositionC: # constituents needed to completely describe the composition;P: # phases present at equilibrium.Examples: x, z: F = 1 - 2 + 1 = 0 (invariant points); y: F = 2 - 3 + 1 = 0:e: F = 1 - 1 + 1 = 1 (univariant); liquid: F = 2 - 1 + 1 = 2 (bivariant)
Compositionsof PhasesinCu-NiPhaseDiagramDeterminethecompositionof each phase ina Cu-40%Nialloyat1300C,1270C,1250C.and120015001453T<1085oC:Cu&Niaremutuallysolubleinsolidstate-complete1400solubilityL→bothhavethesameFCCα+401300structures;atomicradii and1270°3750electronegativities are nearly3245identical;similarvalences化合价1250°120040→isomorphousa1100Tielinesandphasecompositions1085foraCu-40%Nialloyatseveraltemperatures1000Ni20406080CuWeightpercent nickel
Compositions of Phases in Cu-Ni Phase Diagram Determine the composition of each phase in a Cu-40% Ni alloy at 1300℃, 1270 ℃, 1250 ℃, and 1200 ℃
Determinationof PhaseCompositionsCu-Ni:Tie-lines for Two-phase Regions1.Atie lineis constructedacrossthe two-phase region at thetemperatureofthealloy1300Lquid2.The intersections of the tie lineDsanedTielinea-Liquidand the phase boundaries oneithersidearenoted.ua3.PerpendicularsaredroppedLiquid1200fromtheseintersections to thehorizontalcompositionaxis,fromwhichthecompositionofeachofthe respective phases is read.20305040CCo31.5wt%Niompeition(w%Ni)42.5wt%Ni68.5%Cu57.5wt%Cu
Determination of Phase Compositions Cu-Ni: Tie-lines for Two-phase Regions
The Lever Rule Tie line - connects the phases in equilibrium witheach other - essentially an isothermT(℃)How much of eachphase?tie lineiauidusThink of it as a lever (teeter-totter)1300L(liquid)L+αM.M,BsolidusTBαL+α(solid)1200LRiSSH502030CLC。40CαM_.S=M,·Rwt% NiAdaptedfromFig.9.3(b)Callister7e.sM,RC.-CoC。-C,W,W.OM, +M。R+SR+SC. -CC-CL