材料科学基础辅导与习题-上交课件 02ch2-3.1

§2-3参考书胡赓祥等，金属学，上海科学技术出版社，1980

包永千，金属学基础，冶金工业出版社，1986

卢光熙等，金属学教程，上海科学技术出版社，1985潘金生等，材料科学基础，清华大学出版社，1995

1§2-3合金相的晶体结构

1.概述2.固溶体3.化合物4.合金相的结构符号21.概述1.1合金化的目的1.2基本概念3

1.1合金化的目的纯金属因性能有一定的局限性,故应用范围受到了限制

合金化是提高纯金属性能的最主要的途径

Mostpuremetalsaresoftandnotveryusefulintheirpurestate.Thereforeinordertoincreasepropertieslikestrength,hardnessandcorrosionresistancewemixtwoormorepuremetalstogethertogiveusanalloy.EverydayexamplesofalloysincludeBronzewhichisanalloyofCopperandTinwheretheTincontentisusuallylessthan20%.

4

合金化举例材料工业纯铁40Cr60Si2CrVA工业纯铝LD10σb(Mpa)2001000190050480材料工业纯铜H70QBe2LC6σb(Mpa)230660140068056789Bare-aluminiumoverhead-conductors99%pureAl(1XXX)Foragivenweight,purealuminiumhasthehighestconductivitythananyelement.SpecificconductivitytwicethatofCu.1011121314beveragecans(3XXX)Al-MnorAl-Mn-Mg15165XXXmagnesium-containing172XXX(Cu-containing,500MPa)7XXX(Zn+Mg+Cu-containing,600MPa)181.2基本概念1.2.1合金1.2.2组元1.2.3合金相1.2.5组织1.2.6合金相的分类19StrengthThemaincontributionstothestrengthofasteelcomefrom:Thesefactorsarecontrolledbythechemistryofthesteelandtheprocessingrouteusedtoproducethefinalcomponent.Alloftheseaspectsneedtobetakenintoaccountwhenselectingordesigningasteelforagivenapplication.Effect

of

grain

size

Effect

of

microstructure

Effect

of

solid

solution

strengthening

Effect

of

precipitates

Effect

of

dislocations20Forferriteandpearlitesteelsrelationshipsbetweenyield/tensilestrengthandvariouscompositionalandmicrostructuralfactorshavebeendeveloped.Theseareusefulinthattheyshowgeneralcharacteristics,althoughtheyareunabletoincorporateallfactorsthatinfluencestrengthinmodernsteels,forexampleprecipitationstrengthening.Examplesoftheserelationshipsaregivenbelow:YS(MPa)=53.9+32.3Mn+83.2Si+354Nf+17.4d-1/2

UTS(MPa)=294+27.7Mn+83.2Si+3.85pearlite%+7.7d-1/2

Alloyingadditioninwt%,distheferritegrainsizeinmm,Nfisthefreenitrogencontent

21RollingThemostwidelyusedformingprocessinwhichthethicknessofamaterialisreducedbypassingbetweentworolls.Hot-rollingisusedforlargeramountsofdeformation.Cold-rollingisusedtooptimizethemechanicalpropertiesandsurfacefinish.22AnnealingAheattreatmentdesignedtosoftenametaloralloy.Annealingisassociatedwithrecovery,recrystallisationand/orgraingrowth.23Whatisamicrostructure?Metalsarecrystallinewheninthesolidform.Thecrystalstructureofasolidmetalreferstotheinternalstructureorarrangementoftheatomsinanordered,repeating,threedimensionalpattern.Normalmetallicobjectsarepolycrystalline,whichmeanstheyconsistofanaggregateofmanyverysmallcrystals.Thesecrystalsarecalledgrains.24Somemetallicobjects,suchascastings,haveverylargegrainsthatcanberesolvedwiththenakedeyeandthesestructuresarereferredtoasmacrostructures.Typically,thegrainsofametalobjectareverysmall,andcannotbeviewedwiththenakedeye.Thestructuralfeaturesofthesmallgrainsareobservedusinganopticalmicroscopeormetallograph,oranelectronmicroscope,atmagnificationsgreaterthan100times.Structuresrequiringthisrangeofmagnificationfortheirexaminationarecalledmicrostructures.

25Whyisthemicrostructureofamaterialimportant?Themostimportantaspectofanyengineeringmaterialisitsstructure.Thestructureofamaterialisrelatedtoitscomposition,properties,processinghistoryandperformance.Andtherefore,studyingthemicrostructureofamaterialprovidesinformationlinkingitscompositionandprocessingtoitspropertiesandperformance.Interpretationofmicrostructuresrequiresanunderstandingoftheprocessesbywhichvariousstructuresareformed.PhysicalMetallurgyisthesciencewhichprovidesmeaningfulexplanationsofthemicrostructures,throughunderstandingwhatishappeningisinsideametalduringthevariousprocessingsteps.Metallographyisthescienceofpreparingspecimens,examiningthestructureswithamicroscopeandinterpretingthemicrostructures.26Thestructuralfeaturespresentinamaterialareafunctionofthecompositionandformofthestartingmaterial,andanysubsequentheattreatmentsandorprocessingtreatmentsthematerialreceives.Microstructuralanalysisisusedtogaininformationonhowthematerialwasproducedandthequalityoftheresultingmaterial.Microstructuralfeatures,suchasgrainsize,inclusions,impurities,secondphases,porosity,segregationorsurfaceeffects,areafunctionofthestartingmaterialandsubsequentprocessingtreatments.27WhatisMicrostructuralAnalysisusedfor?

Macrostructuralandmicrostructuralexaminationtechniquesareemployedinareassuchasroutinequalitycontrol,failureanalysisandresearchstudies.Inqualitycontrol,microstructuralanalysisisusedtodetermineifthestructuralparametersarewithincertainspecifications.Itisusedasacriterionforacceptanceorrejection.Themicrostructuralfeaturessometimesconsideredaregrainsize,amountofimpurities,secondphases,porosity,segregationordefectspresent.Theamountorsizeofthesefeaturescanbemeasuredandquantified,andcomparedtotheacceptancecriterion.Varioustechniquesforquantifyingmicrostructuralfeatures,suchasgrainsize,particleorporesize,volumefractionofaconstituent,andinclusionrating,areavailableforcomparativeanalysis.28Microstructuralanalysisisusedinfailureanalysistodeterminethecauseoffailure.Failurescanoccurduetoimpropermaterialselectionandpoorqualitycontrol.Microstructuralexaminationofafailedcomponentisusedtoidentifythematerialandtheconditionofthematerialofthecomponent.Throughmicrostructuralexaminationonecandetermineifthecomponentwasmadefromspecifiedmaterialandifthematerialreceivedtheproperprocessingtreatments.Failureanalysis,examiningthefracturesurfaceofthefailedcomponent,providesinformationaboutthecauseoffailure.Failuresurfaceshavebeenwelldocumentedovertheyearsandcertainfeaturesareassociatedwithcertaintypesoffailures.Usingfailureanalysisitispossibletodeterminethetypeofstressthatcausedthecomponenttofailandoftentimesdeterminetheoriginofthefracture.29Microstructuralanalysisisusedinresearchstudiestodeterminethemicrostructuralchangesthatoccurasaresultofvaryingparameterssuchascomposition,heattreatmentorprocessingsteps.Typicalresearchstudiesincludemicrostructuralanalysisandmaterialspropertytesting.Throughtheseresearchprogramstheprocessing-structure-propertyrelationshipsaredeveloped.30WhatisMetallography?

Metallographyisthestudyofthestructureofmetals.Itincludesthetechniquesusedtopreparespecimensforexamination,examiningthespecimenandinterpretingthestructures.Specimenpreparationisanimportantpartofmetallography.Aspecimenmustbeappropriatelypreparedtoensurecorrectobservationandinterpretationofthemicrostructure.Specimenpreparationconsistsofsampleselection,sectioning,grinding,polishing,andetching.Adequatesampleselectionprovidesastatisticallyreliabledescriptionofthematerialquality.Thenumber,locationandorientationofthesamplesexaminedareimportantparametersinsampleselection.Sectioning,grindingandpolishingareusedtoprepareaflatspecimenwithamirrorlikefinish.Caremustbetakenduringsamplepreparationnottointroduceartifactswhichleadtoinvalidmicrostructureinterpretations.31Sometimesitisbeneficialtoexaminethespecimenintheaspolishedcondition.Theaspolishedconditionisusefulforexaminingthemicrostructuresofmaterialswhoseconstituentsexhibitlargedifferencesinlightreflectivityafterpolishing.Porosityandinclusionsareexamplesoffeaturesthatareeasilyobservedintheaspolishedcondition.Butmostmaterialsareetchedtorevealthemicrostructure.Etchingisacontrolledcorrosionprocessresultingformelectrolyticactionbetweensurfaceareasofdifferentpotential.Etchingrevealsthemicrostructureofamaterialbyselectivedissolutionofthestructure.Specimensarethenexaminedusingopticalandelectronmicroscopes.Therearealsomanyothertechniquesusedtocharacterizethestructureofmetals,butherewillconcentrateonmicrostructuralcharacterization.3233341.2.1合金合金是由两种或两种以上的金属或金属与非金属,经过熔炼、烧结或其它方法组合而成并具有金属特性的物质

35AlloyAmetal-likesubstanceproducedbymixingtwoormoremetalsornon-metals.Ceramicscanalsobemixedtoformalloys.Abinaryalloycontainstwocomponents.Aternaryalloycontainsthree.36WhatisanAlloy?

Analloyconsistsofamixtureofapuremetalandoneormoreotherelements.

Often,theseotherelementswillbemetals.

Forexample,brassisanalloyofcopperandzinc.

Inothercases,ametalwillbealloyedwithanon-metal.

Themostimportantexampleofalloyinginvolvingadditionofanon-metalwouldbe(plain-carbon)steelswhichconsistofironalloyedwithcarbon371.2.2组元组元是组成合金的最简单、最基本而且能独立存在的物质,纯元素是组元,化合物也可以是组元合金的分类38ComponentAlsoConstituent.Theindividualchemicalsubstances(elementsorcompounds)presentinanalloysystem.ThecomponentsincarbonsteelareFeandC.InbronzetheyareCuandSn.Constituent-Componentofanalloyorotherchemicalsubstance.391.2.3合金相相是从组织角度说明合金中具有同一聚集状态、同一结构,以及成分、性质完全相同的均匀组成部分

合金的分类40PhaseAphaseisaportionofa(alloy)systemthatishomogeneousinbothitsPHYSICALandCHEMICALproperties.Asinglephasecanbemadeupofmorethanonecomponent.Cu-Nialloysforexamplesolidifytogiveasinglephase(solidsolution).Conversely,itispossibleforasinglecomponenttoexistastwophases-e.g.liquidandsolidphasesareinequilibriumatthemeltingtemperature.41ScaleofmicrostructureThescaleofmicrostructure(nm,mm,mm,etc.)isoneofthethreemostimportantfactorsthatdetermineamaterial'sproperties.Theothertwoareconstitutionandphasemorphology.42PhasemorphologyTheshapeofphasesinamaterial.Togetherwithconstitutionandscale,thephasemorphology(globular,plate-like,rod-like,etc.)ofamaterialiscriticalindeterminingitsproperties.43441.2.4组织组织指的是在外界因素、成分等条件一定的情况下,组成合金的不同成分、结构和性能的相的总体Thescaleofmicrostructure,constitutionandphasemorphologyarethethreemostimportantfactorsthatdetermineamaterial'sproperties.45NominalComposition:Cu99.5,Be1.6-1.79

AlloyFamily:HighcopperalloysAlloy:C17000ProductForm:Temper:Processing:AscastMaterial:BerylliumcopperEtchant:Source:UniversityofFloridaScaleLineLength~500Microns46HighCopperAlloys:C17200-strip47AlloyFamily:HighCopperAlloysAlloy:C17200ProductForm:StripTemper:TD04Processing:Cast,hotrolled,intermediateannealed,coldrolled,solutionannealedandcoldrolled37%toHardtemperEtchant:Ammonium

persulfate/ammoniumhydroxide;1partNH40H(ammoniumhydroxide)(conc)and2parts(NH4)2S208(arnmonium

persulfate),2.5%indistilledwaterNominalComposition:Be1.80-2.00,Co+Ni0.20min,Co+Ni+Fe0.6

max,Pb0.02max,Cu+SumofNamedElements99.5min

Description:Solutionannealedat790C(1450F)andcoldrolled37%tofullhardtemper.Longitudinalsectionshowselongatedgrainsofalphaphaseandcobaltberyllides.48CopperberylliumalloysCopperberylliumalloysareusedfortheirhighstrengthandgoodelectricalandthermalconductivities.Therearetwogroupsofcopperberylliumalloys,highstrengthalloysandhighconductivityalloys.Thewrought锻造的

highstrengthalloyscontain1.6to2.0%berylliumandapproximately0.3%cobalt.Thecast,high-strengthalloyshaveberylliumconcentrationsupto2.7%.Thehighconductivityalloyscontain0.2-0.7%berylliumandhigheramountsofnickelandcobalt.Thesealloysareusedinapplicationssuchaselectronicconnectorcontacts,electricalequipmentsuchasswitchandrelayblades,controlbearings,housingsformagneticsensingdevices,nonsparkingapplications,smallsprings,highspeedplasticmoldsandresistanceweldingsystems.49Castberylliumcoppersarefrequentlyusedforplasticinjectionmolds注模.Thecastmaterialshavehighfluidityandcanreproducefinedetailsinmasterpatterns母模.Theirhighconductivityenableshighproductionspeed,whiletheirgoodcorrosionandoxidationresistancepromoteslongdielife.50Thehighstrengthofthecopperberylliumalloysisattainedbyagehardeningorprecipitationhardening.Theageorprecipitationhardeningresultsfromtheprecipitationofaberylliumcontainingphasefromasupersaturatedsolidsolutionofmostlypurecopper.Theprecipitationoccursduringtheslowcoolingofthealloysbecausethesolubilityofberylliuminalphacopperdecreaseswithdecreasingtemperature.5152535455565758dendriticstructure59601.2.5合金相的分类⑴固溶体⑵化合物⑶夹杂物61SolidSolutionsandIntermetallicCompounds

Inmanycases,metalsarequitesolubleinothermetals.

Forexample,solidcopperandsolidnickelarefullysolubleineachother.

Thistypeofperfectsolidsolubilityisasideeffectofhavingfreeelectrons.

Sincetheelectronsarefreetomove,theexactnumberofvalenceelectronspossessedbyanygivenatomshouldn’tmatter.

Thusametalshouldbeabletodissolveanothermetalandproducea“solid-solution”inwhichonemetalservesasthesolventandtheotherasthesolute.62Inpractice,however,notallmetalsaresolubleinothermetals.

Thus,insteadofasolid-solutionanewphase,an“intermetalliccompound”,withastructuredifferentfromthatofanyofitsconstituentmetalscanbeproduced.

Forexample,nickelwilldissolvesomealuminum,sothatatlowaluminumcontentsasolidsolutionisproduced.

However,iflargeramountsofaluminumareadded,thenaseriesofintermetalliccompounds(forexampleNi3AlandNiAl)areproduced.

63IntroductionTheextenttowhichthecomponentsofanalloyaremiscibledependsontheinteractionbetweentheatoms:Ifthespeciesdonottendtobondtoeachother,thenseparatephaseswillformwithlimitedmiscibilityIfstrongmutualattractionoccurs,asinglecrystalofadifferentstructurecanform,suchasinintermetalliccompounds

Ifthereislittledifferencebetweenlikeandunlikebonds,thenasolidsolutioncanoccur,overawiderangeofchemicalcompositions64SolidsolutionInthesesolidsolutions,differenttypesofatomsormoleculesexistinthesamecrystallattice.AgoodexampleofasolidsolutionistheCu-Nisystem,forwhichthephasediagramisshownbelow.Bothmetalsarecompletelysolubleineachother.Theaphaseisasubstitutionalsolidsolution.ThisoccursbecauseboththeCuandNiformfacecentredcubicstructures,andhavesimilaratomicradii,electronegativitiesandvalences.Copperandnickelshowverydifferentphysicalpropertiesintheirpurestates,andtheaphaseprovidesacontinuouschangebetweentheextremes.65⑴固溶体固溶体:以合金中某一组元为溶剂,其它组元为溶质,所形成的与溶剂有相同晶体结构、晶格常数稍有变化的固相称为固溶体66SolidsolutionAnarrangementofdifferentatomormoleculetypeswithinthesamecrystallattice.Solidsolutionstendtoformwhentheinteractionbetweenthecomponentatomsissmall,i.e.theyneitherattractnorrepeleachother.

Ahomogeneouscrystallinestructureinwhichoneormoretypesofatomsormoleculesmaybepartlysubstitutedfortheoriginalatomsandmoleculeswithoutchangingthestructure.

67⑵化合物化合物是由两种或多种组元按一定比例构成一个新的点阵,它既不是溶剂的点阵,也不是溶质的点阵

Compound-(chemistry)asubstanceformedbychemicalunionoftwoormoreelementsoringredientsindefiniteproportionbyweightSynonymschemicalcompound682.固溶体2.1固溶体的特征2.2固溶体的分类2.3置换固溶体2.4间隙固溶体2.5固溶体的微观不均匀性2.6固溶体的性能特点692.1固溶体的特征2.1.1溶质和溶剂原子占据一个共同的布拉菲点阵,且此点阵类型和溶剂点阵类型相同

2.1.2有一定的成分范围,故通常固溶体不能用一个化学式来表示

2.1.3具有比较明显的金属性质,说明固溶体中的结合键主要是金属键

702.2固溶体的分类2.2.1依溶质在溶剂中位置2.2.2依溶解度大小2.2.3依溶质的分布特点2.2.4依溶剂组元的类型

71TypesofsolidsolutionSubstitutionalsolidsolution:chemicalvariationisachievedsimplybysubstitutingonetypeofatominthestructurebyanother.Coupledsubstitution:thisissimilartothesubstitutionalsolidsolution,butinacompoundcationsofdifferentvalenceareinterchanged.Tomaintainchargebalance,twocoupledcationsubstitutionsmusttakeplace.Omissionsolidsolution:chemicalvariationisachievedbyomittingcationsfromcationsitesthatarenormallyoccupied.Interstitialsolidsolution:chemicalvariationisachievedbyaddingatomsorionstositesinthestructurethatarenotnormallyoccupied.722.2.1依溶质在溶剂中位置73SolidSolution

Asolidsolutionoccurswhenwealloytwometalsandtheyarecompletelysolubleineachother.Ifasolidsolutionalloyisviewedunderamicroscopeonlyonetypeofcrystalcanbeseen

justlikeapuremetal.Solidsolutionalloyshavesimilarpropertiestopuremetalsbutwithgreaterstrengthbutarenotasgoodaselectricalconductors.Theusualformsofsolidsolutionare.SubstitutionalSolidsolutionInterstitialsolidsolution

742.2.2依溶解度大小无限固溶体(连续固溶体)

溶质和溶剂元素可以任何比例相互溶解.其合金成份可从一个组元连续改变到另一个组元而不出现其它合金相

有限固溶体(端际固溶体)

在相图中的位置靠近两端的纯组元

75PartialsolubilityThepartialsolubilityequilibriumdiagramisderivedfromtheprevioustwodiagramsthatindicatedsolubleandinsolublestates.Fewalloysexhibittotalinsolubilityortotalsolubilityandmanymetalscombinetoformapartialsolubilitysystem.Theendsofthetotallysolublesystemareamalgamatedwiththecentralportionoftheinsolubleoreutecticsystemtoformthepartiallysolubleinthesolidstateequilibriumdiagramasshownhere.76Lines"ae"and"eb"(grey)arethe

liquiduslines.Lines"ac"and"bd"(maroon)arethe

Soliduslines.

Twonewlinesexistinthisdiagram"cf"and"dg"(inblue)andthesearetheSolvuslineswhichshowthesolubilityofthetwometalsineachother.77782.2.3依溶质的分布特点无序固溶体溶质原子在溶剂晶格中的分布是随机的,完全无序的(实质是近程有序分布)有序固溶体

溶质原子在大范围内完全有序分布,即长程有序结构.它在

X射线衍射图上会出现附加的线条,称为超结构线,故有序固溶体也称为超结构或超点阵

792.2.4依溶剂组元的类型第一类固溶体以纯金属元素为溶剂而形成的固溶体第二类固溶体以化合物为溶剂而形成的固溶体

802.3置换固溶体

影响其固溶度大小的因素有:2.3.1

晶体结构因素2.3.2

尺寸因素2.3.3

电负性差因素2.3.4

电子浓度因素81FactorsaffectingtheextentofsolidsolutionAtomic/ionicsize:Iftheatomsorionsinasolidsolutionhavesimilarionicradii,thenthesolidsolutionisoftenveryextensiveorcomplete.Generally,ifthesizedifferenceislessthanabout15%,thenextensivesolidsolutionispossible.Forexample,Mg2+andFe2+haveasizemismatchofonlyabout7%,andcompletesolidsolutionbetweenthesetwoelementsisobservedinawiderangeofminerals.However,thereisa32%sizedifferencebetweenCa2+andMg2+,andweexpectverylittlesubstitutionofMgforCatooccurinminerals.2.Temperature:3.Structuralflexibility:4.Cationcharge:82Factorsaffectingtheextentofsolidsolution2.Temperature:Hightemperaturesfavourtheformationofsolidsolutions,sothatendmemberswhichareimmiscibleatlowtemperaturemayformcompleteormoreextensivesolidsolutionswitheachotherathightemperature.Hightemperaturespromotegreateratomicvibrationandopenstructures,whichareeasiertodistortlocallytoaccommodatedifferently-sizedcations.Mostimportantly,solidsolutionshaveahigherentropythantheendmembers,duetotheincreaseddisorderassociatedwiththerandomlydistributedcations,andathightemperatures,the-TStermintheGibb'sfreeenergystabilisesthesolidsolution.83Factorsaffectingtheextentofsolidsolution3.Structuralflexibility:Althoughcationsizeisausefulindicatoroftheextentofsolidsolutionbetweentwoendmembers,muchdependsontheabilityoftherestofthestructuretobendbonds(ratherthanstretchorcompressthem)toaccommodatelocalstrains.4.Cationcharge:Heterovalentsubstitutions(i.e.thoseinvolvingcationswithdifferentcharges)rarelyleadtocompletesolidsolutionsatlowtemperatures,sincetheyundergocomplexcationorderingphasetransitionsand/orphaseseparationatintermediatecompositions.Theseprocessesaredrivenbytheneedtomaintainlocalchargebalanceinthesolidsolutionaswellastoaccommodatelocalstrain.84SubstitutionalSolidsolutionThenameofthissolidsolutiontellsyouexactlywhathappensasatomsoftheparentmetal(orsolventmetal)arereplacedorsubstitutedbyatomsofthealloyingmetal(solutemetal)Inthiscase,theatomsofthetwometalsinthealloy,areofsimilarsize.Hereweseethebrownatomshavebeenreplacedorsubstitutedbytheblueatoms.85862.3.1晶体结构因素⑴晶体结构相同是组元间形成无限固溶体的必要条件

⑵对有限固溶体,若溶质与溶剂的晶体结构相同,则溶解度通常较大,否则,反之872.3.2尺寸因素⑴原子尺寸因素,是指形成固溶体的溶质原子半径RB与溶剂原子半径RA的相对差值大小,常以⊿R表示:

⊿R＝（RA－RB）/RA×100%⑵⊿R＜15﹪时,才可能形成溶解度较大甚至无限溶解的固溶体;反之,则溶解度非常有限

88⑴原子尺寸因素形成置换固溶体时的点阵畸变

89⑵⊿R＜15﹪902.3.3电负性差因素⑴电负性与原子序数的关系

⑵电负性差与化合物稳定性的关系91⑴电负性与原子序数Z的关系同周期元素，电负性随Z的增大而增大；同族元素，电负性随Z增大而减小。

92⑵电负性差与化合物稳定性的关系932.3.4电子浓度因素⑴电子浓度⑵原子价⑶极限电子浓度94⑴电子浓度

是指固溶体中价电子数目e与原子数目a之比.假设溶质原子价为v,溶剂原子价为V,溶质元素的原子百分数为x,则该固溶体的电子浓度为:

e/a＝[V(100－x)＋vx]/100

95⑵原子价1这里的原子价表示形成合金时,每一原子平均贡献出的公有电子数(或参加结合键的电子数),此数值与该元素在化学反应时表现出的价数不尽一致.过渡族元素的原子价取为零.96⑵原子价2元素名称原子价元素名称原子价CuAuAg+1FeCoNi0BeMgZnCdHg+2Ru

RhPd0AlInAg+3OsIrPt0Sn

Si

Ge

Pb+4CeLaPrNd0AsSbBiP+597⑶极限电子浓度有些合金,固溶度的主要因素是电子浓度,它们往往存在一极限电子浓度,此时固溶度最大,超过极限电子浓度,固溶体就不稳定,便会形成新相.溶质原子价越高,溶解度极限越小例如Zn、Ga、Ge、As分别为2～5价，它们在Cu中的固溶度极限以Zn最大,为38﹪,Ga为20﹪;

Ge为12﹪;As最小,仅为7.0﹪当溶剂为l价面心立方金属时,溶入

2价或

2价以上溶质元素时最大溶解度极限对应的极限电子浓度为1.36;l价体心立方金属为溶剂时,此极限值为1.48,而以密排六方金属为溶剂时,此极限值为1.7598992.4间隙固溶体2.4.1间隙固溶体的概念2.4.2形成间隙固溶体的条件2.4.3间隙固溶体的固溶度100InterstitialsolidsolutionIninterstitialsolidsolutionstheatomsoftheparentorsolventmetalarebiggerthantheatomsofthealloyingorsolutemetal.Inthiscase,thesmalleratomsfitintointersticesi.espacesbetweenthelargeratoms.Thepurpleatomsaresmallenoughtofitintothespacesbetweenthelargersolventatoms.

1011022.4.1间隙固溶体的概念

当原子半径比较小的非金属元素作为溶质溶入金属或化合物的溶剂中时,这些小的溶质原子不占有溶剂晶格的结点位置,而存在于间隙位置,形成间隙固溶体.

1032.4.2形成间隙固溶体的条件溶剂:大多是过渡族元素溶质:一般是原子半径小于0.lnm的一些非金属元素,即氢0.046、氧0.061、氮0.071、碳0.077、硼0.097等

保证⊿R＞41﹪电负性差不大1042.4.3间隙固溶体的固溶度固溶度都很小

原因是溶质原子存在于间隙位置上引起点阵畸变较大,所以它们不仅不可能填满全部间隙,而且一般固溶度都很小

γ-Fe:八面体间隙α-Fe:八面体间隙CN填满实际填满实际γ-Fe

5