材料科學(xué)基礎(chǔ)-第7章2合金相圖

1二元共晶相圖Pb-Sb、Pb-Sn、Ag-Cu、Al-Si、Zn-Sn等合金相圖都屬于共晶相圖，在Mg-Al及Fe-Fe3C相圖中也包含有共晶部分。共晶反應(yīng)；共晶組織（共晶體）Section7.4二元共晶相圖及其合金的結(jié)晶圖7-13Pb-Sn二元相圖2點(diǎn)、線、區(qū)分析、固溶體；最大溶解度；室溫下溶解度；熔點(diǎn)，共晶點(diǎn)三相共存水平線（區(qū)）邊際（端部）固溶體合金；共晶合金；亞共晶合金；過(guò)共晶合金相律應(yīng)用7.4.1二元共晶相圖分析圖7-13Pb-Sn二元相圖3Solvus-Asolubilitycurvethatseparatesasingle-solidphaseregionfromatwo-solidphaseregioninthephasediagram.Isopleth-Alineonaphasediagramthatshowsconstantchemicalcomposition.Hypoeutecticalloy-Analloycompositionbetweenthatoftheleft-hand-sideendofthetielinedefiningtheeutecticreactionandtheeutecticcomposition.Hypereutecticalloys-Analloycompositionbetweenthatoftheright-hand-sideendofthetielinedefiningtheeutecticreactionandtheeutecticcomposition.TheEutecticPhaseDiagram4邊際（端部）固溶體，二次結(jié)晶→Ⅱ共晶合金亞共晶合金過(guò)共晶合金7.4.2典型合金的平衡結(jié)晶過(guò)程及室溫平衡組織5Figurethelead-tinequilibriumphasediagram.6FigureSolidificationandmicrostructureofaPb-2%Snalloy.Thealloyisasingle-phasesolidsolution.7FigureSolidification,precipitation,andmicrostructureofaPb-10%Snalloy.Somedispersionstrengtheningoccursastheβsolidprecipitates.8Determine(a)thesolubilityoftininsolidleadat100oC,(b)themaximumsolubilityofleadinsolidtin,(c)theamountofβthatformsifaPb-10%Snalloyiscooledto0oC,(d)themassesoftincontainedintheαandβphases,and(e)massofleadcontainedintheαandβphases.AssumethatthetotalmassofthePb-10%Snalloyis100grams.ExamplePhasesintheLead–Tin(Pb-Sn)PhaseDiagram9FigureSolidification,precipitation,andmicrostructureofaPb-10%Snalloy.Somedispersionstrengtheningoccursastheβsolidprecipitates.10ExampleSOLUTION(a)The100oCtemperatureintersectsthesolvuscurveat5%Sn.Thesolubilityoftin(Sn)inlead(Pb)at100oCthereforeis5%.(b)Themaximumsolubilityoflead(Pb)intin(Sn),whichisfoundfromthetin-richsideofthephasediagram,occursattheeutectictemperatureof183oCandis97.5%Sn.(c)At0oC,the10%Snalloyisinaα+βregionofthephasediagram.Bydrawingatielineat0oCandapplyingtheleverrule,wefindthat:11ExampleSOLUTION(Continued)(d)ThemassofSnintheαphase=2%Sn

91.8gofαphase=0.02

91.8g=1.836g.Sincetin(Sn)appearsinboththeαandβphases,themassofSnintheβphasewillbe=(10–1.836)g=8.164g.(e)MassofPbintheαphase=98%Sn

91.8gofαphase=0.98

91.8g=89.964gMassofPbintheβphase=90-89.964=0.036g.12FigureSummaryofcalculations13FigureSolidificationandmicrostructureoftheeutecticalloyPb-61.9%Sn.14FigureThecoolingcurveforaeutecticalloyisasimplethermalarrest,sinceeutecticsfreezeormeltatasingletemperature.15Figure(a)Atomredistributionduringlamellargrowthofalead-tineutectic.Tinatomsfromtheliquidpreferentiallydiffusetotheβplates,andleadatomsdiffusetotheαplates.(b)Photomicrographofthelead-tineutecticmicroconstituent(x400).16ExampleAmountofPhasesintheEutecticAlloy(a)Determinetheamountandcompositionofeachphaseinalead-tinalloyofeutecticcomposition.(b)Calculatethemassofphasespresent.(c)Calculatetheamountofleadandtinineachphase,assumingyouhave200gofthealloy.ExampleSOLUTION(a)Theeutecticalloycontains61.9%Sn.17ExampleSOLUTION(Continued)(b)Atatemperaturejustbelowtheeutectic:Themassoftheαphasein200gofthealloy=massofthealloy

fractionoftheaphase=200g

0.4535=90.7gTheamountoftheβphasein200gofthealloy=(massofthealloy

massoftheaphase)=200.0g

90.7g=109.3g18ExampleSOLUTION(Continued)-MassofPbintheαphase=massoftheaphasein200g

(concentrationofPbinα)=(90.7g)

(1–0.190)=73.467g-MassofSnintheαphase=massoftheaphase-massofPbintheaphase=(90.7–73.467g)=17.233g-MassofPbinβphase=massofthebphasein200g

(wt.fractionPbinβ)=(109.3g)

(1–0.975)=2.73g-MassofSnintheβphase=totalmassofSn–massofSnintheαphase=123.8g–17.233g=106.57g19FigureSummaryofcalculations20FigureThesolidificationandmicrostructureofahypoeutecticalloy(Pb-30%Sn).21Figure(a)Ahypoeutecticlead-tinalloy.(b)Ahypereutecticlead-tinalloy.Thedarkconstituentisthelead-richsolidα,thelightconstituentisthetin-richsolidβ,andthefineplatestructureistheeutectic(x400).22ExampleDeterminationofPhasesandAmountsinaPb-30%SnHypoeutecticAlloyForaPb-30%Snalloy,determinethephasespresent,theiramounts,andtheircompositionsat300oC,200oC,184oC,182oC,and0oC.23ExampleSOLUTION24ExampleMicroconstituentAmountandCompositionforaHypoeutecticAlloyDeterminetheamountsandcompositionsofeachmicroconstituentinaPb-30%Snalloyimmediatelyaftertheeutecticreactionhasbeencompleted.ExampleSOLUTIONAtatemperaturejustabovetheeutectic—say,184oC—theamountsandcompositionsofthetwophasesare:25FigureThecoolingcurveforahypoeutecticPb-30%Snalloy.26EutecticColonySizeInterlamellarSpacingAmountofEutecticMicrostructureoftheEutecticStrengthofEutecticAlloys27Figure(a)Coloniesinthelead-tineutectic(x300).(b)Theinterlamellarspacinginaeutecticmicrostructure.28FigureTheeffectofgrowthrateontheinterlamellarspacinginthelead-tineutectic.29ExampleDesignofaDirectionalSolidificationProcessDesignaprocesstoproduceasingle‘‘grain’’ofPb-Sneutecticmicroconstituentinwhichtheinterlamellarspacingis0.00034cm.ExampleSOLUTIONWecoulduseadirectionalsolidification(DS)processtoproducethesinglegrain,whilecontrollingthegrowthratetoassurethatthecorrectinterlamellarspacingisachieved. Figureshowshowwemightachievethisgrowthrate.ThePb-61.9%Snalloywouldbemeltedinamoldwithinafurnace.Themoldwouldbewithdrawnfromthefurnaceattherateof0.00025cm/s,withthemoldquenchedwithawatersprayasitemergesfromthefurnace.30FigureDirectionalsolidificationofaPb-Sneutecticalloy:(a)Themetalismeltedinthefurnace,and(b)themoldisslowlywithdrawnfromthefurnaceandthecastingiscooled31FigureTheeffectofthecompositionandstrengtheningmechanismonthetensilestrengthoflead-tinall