材料科學(xué)基礎(chǔ)輔導(dǎo)與習(xí)題-上交課件 02ch2-3.1

§2-3參考書胡賡祥等，金屬學(xué)，上?？茖W(xué)技術(shù)出版社，1980

包永千，金屬學(xué)基礎(chǔ)，冶金工業(yè)出版社，1986

盧光熙等，金屬學(xué)教程，上?？茖W(xué)技術(shù)出版社，1985潘金生等，材料科學(xué)基礎(chǔ)，清華大學(xué)出版社，1995

1§2-3合金相的晶體結(jié)構(gòu)

1.概述2.固溶體3.化合物4.合金相的結(jié)構(gòu)符號21.概述1.1合金化的目的1.2基本概念3

1.1合金化的目的純金屬因性能有一定的局限性,故應(yīng)用范圍受到了限制

合金化是提高純金屬性能的最主要的途徑

Mostpuremetalsaresoftandnotveryusefulintheirpurestate.Thereforeinordertoincreasepropertieslikestrength,hardnessandcorrosionresistancewemixtwoormorepuremetalstogethertogiveusanalloy.EverydayexamplesofalloysincludeBronzewhichisanalloyofCopperandTinwheretheTincontentisusuallylessthan20%.

4

合金化舉例材料工業(yè)純鐵40Cr60Si2CrVA工業(yè)純鋁LD10σb(Mpa)2001000190050480材料工業(yè)純銅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組元1.2.3合金相1.2.5組織1.2.6合金相的分類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合金合金是由兩種或兩種以上的金屬或金屬與非金屬,經(jīng)過熔煉、燒結(jié)或其它方法組合而成并具有金屬特性的物質(zhì)

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

Analloyconsistsofamixtureofapuremetalandoneormoreotherelements.

Often,theseotherelementswillbemetals.

Forexample,brassisanalloyofcopperandzinc.

Inothercases,ametalwillbealloyedwithanon-metal.

Themostimportantexampleofalloyinginvolvingadditionofanon-metalwouldbe(plain-carbon)steelswhichconsistofironalloyedwithcarbon371.2.2組元組元是組成合金的最簡單、最基本而且能獨立存在的物質(zhì),純元素是組元,化合物也可以是組元合金的分類38ComponentAlsoConstituent.Theindividualchemicalsubstances(elementsorcompounds)presentinanalloysystem.ThecomponentsincarbonsteelareFeandC.InbronzetheyareCuandSn.Constituent-Componentofanalloyorotherchemicalsubstance.391.2.3合金相相是從組織角度說明合金中具有同一聚集狀態(tài)、同一結(jié)構(gòu),以及成分、性質(zhì)完全相同的均勻組成部分

合金的分類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組織組織指的是在外界因素、成分等條件一定的情況下,組成合金的不同成分、結(jié)構(gòu)和性能的相的總體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鍛造的

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合金相的分類⑴固溶體⑵化合物⑶夾雜物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固溶體固溶體:以合金中某一組元為溶劑,其它組元為溶質(zhì),所形成的與溶劑有相同晶體結(jié)構(gòu)、晶格常數(shù)稍有變化的固相稱為固溶體66SolidsolutionAnarrangementofdifferentatomormoleculetypeswithinthesamecrystallattice.Solidsolutionstendtoformwhentheinteractionbetweenthecomponentatomsissmall,i.e.theyneitherattractnorrepeleachother.

Ahomogeneouscrystallinestructureinwhichoneormoretypesofatomsormoleculesmaybepartlysubstitutedfortheoriginalatomsandmoleculeswithoutchangingthestructure.

67⑵化合物化合物是由兩種或多種組元按一定比例構(gòu)成一個新的點陣,它既不是溶劑的點陣,也不是溶質(zhì)的點陣

Compound-(chemistry)asubstanceformedbychemicalunionoftwoormoreelementsoringredientsindefiniteproportionbyweightSynonymschemicalcompound682.固溶體2.1固溶體的特征2.2固溶體的分類2.3置換固溶體2.4間隙固溶體2.5固溶體的微觀不均勻性2.6固溶體的性能特點692.1固溶體的特征2.1.1溶質(zhì)和溶劑原子占據(jù)一個共同的布拉菲點陣,且此點陣類型和溶劑點陣類型相同

2.1.2有一定的成分范圍,故通常固溶體不能用一個化學(xué)式來表示

2.1.3具有比較明顯的金屬性質(zhì),說明固溶體中的結(jié)合鍵主要是金屬鍵

702.2固溶體的分類2.2.1依溶質(zhì)在溶劑中位置2.2.2依溶解度大小2.2.3依溶質(zhì)的分布特點2.2.4依溶劑組元的類型

71TypesofsolidsolutionSubstitutionalsolidsolution:chemicalvariationisachievedsimplybysubstitutingonetypeofatominthestructurebyanother.Coupledsubstitution:thisissimilartothesubstitutionalsolidsolution,butinacompoundcationsofdifferentvalenceareinterchanged.Tomaintainchargebalance,twocoupledcationsubstitutionsmusttakeplace.Omissionsolidsolution:chemicalvariationisachievedbyomittingcationsfromcationsitesthatarenormallyoccupied.Interstitialsolidsolution:chemicalvariationisachievedbyaddingatomsorionstositesinthestructurethatarenotnormallyoccupied.722.2.1依溶質(zhì)在溶劑中位置73SolidSolution

Asolidsolutionoccurswhenwealloytwometalsandtheyarecompletelysolubleineachother.Ifasolidsolutionalloyisviewedunderamicroscopeonlyonetypeofcrystalcanbeseen

justlikeapuremetal.Solidsolutionalloyshavesimilarpropertiestopuremetalsbutwithgreaterstrengthbutarenotasgoodaselectricalconductors.Theusualformsofsolidsolutionare.SubstitutionalSolidsolutionInterstitialsolidsolution

742.2.2依溶解度大小無限固溶體(連續(xù)固溶體)

溶質(zhì)和溶劑元素可以任何比例相互溶解.其合金成份可從一個組元連續(xù)改變到另一個組元而不出現(xiàn)其它合金相

有限固溶體(端際固溶體)

在相圖中的位置靠近兩端的純組元

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依溶質(zhì)的分布特點無序固溶體溶質(zhì)原子在溶劑晶格中的分布是隨機的,完全無序的(實質(zhì)是近程有序分布)有序固溶體

溶質(zhì)原子在大范圍內(nèi)完全有序分布,即長程有序結(jié)構(gòu).它在

X射線衍射圖上會出現(xiàn)附加的線條,稱為超結(jié)構(gòu)線,故有序固溶體也稱為超結(jié)構(gòu)或超點陣

792.2.4依溶劑組元的類型第一類固溶體以純金屬元素為溶劑而形成的固溶體第二類固溶體以化合物為溶劑而形成的固溶體

802.3置換固溶體

影響其固溶度大小的因素有:2.3.1

晶體結(jié)構(gòu)因素2.3.2

尺寸因素2.3.3

電負(fù)性差因素2.3.4

電子濃度因素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晶體結(jié)構(gòu)因素⑴晶體結(jié)構(gòu)相同是組元間形成無限固溶體的必要條件

⑵對有限固溶體,若溶質(zhì)與溶劑的晶體結(jié)構(gòu)相同,則溶解度通常較大,否則,反之872.3.2尺寸因素⑴原子尺寸因素,是指形成固溶體的溶質(zhì)原子半徑RB與溶劑原子半徑RA的相對差值大小,常以⊿R表示:

⊿R＝（RA－RB）/RA×100%⑵⊿R＜15﹪時,才可能形成溶解度較大甚至無限溶解的固溶體;反之,則溶解度非常有限

88⑴原子尺寸因素形成置換固溶體時的點陣畸變

89⑵⊿R＜15﹪902.3.3電負(fù)性差因素⑴電負(fù)性與原子序數(shù)的關(guān)系

⑵電負(fù)性差與化合物穩(wěn)定性的關(guān)系91⑴電負(fù)性與原子序數(shù)Z的關(guān)系同周期元素，電負(fù)性隨Z的增大而增大；同族元素，電負(fù)性隨Z增大而減小。

92⑵電負(fù)性差與化合物穩(wěn)定性的關(guān)系932.3.4電子濃度因素⑴電子濃度⑵原子價⑶極限電子濃度94⑴電子濃度

是指固溶體中價電子數(shù)目e與原子數(shù)目a之比.假設(shè)溶質(zhì)原子價為v,溶劑原子價為V,溶質(zhì)元素的原子百分?jǐn)?shù)為x,則該固溶體的電子濃度為:

e/a＝[V(100－x)＋vx]/100

95⑵原子價1這里的原子價表示形成合金時,每一原子平均貢獻(xiàn)出的公有電子數(shù)(或參加結(jié)合鍵的電子數(shù)),此數(shù)值與該元素在化學(xué)反應(yīng)時表現(xiàn)出的價數(shù)不盡一致.過渡族元素的原子價取為零.96⑵原子價2元素名稱原子價元素名稱原子價CuAuAg+1FeCoNi0BeMgZnCdHg+2Ru

RhPd0AlInAg+3OsIrPt0Sn

Si

Ge

Pb+4CeLaPrNd0AsSbBiP+597⑶極限電子濃度有些合金,固溶度的主要因素是電子濃度,它們往往存在一極限電子濃度,此時固溶度最大,超過極限電子濃度,固溶體就不穩(wěn)定,便會形成新相.溶質(zhì)原子價越高,溶解度極限越小例如Zn、Ga、Ge、As分別為2～5價，它們在Cu中的固溶度極限以Zn最大,為38﹪,Ga為20﹪;

Ge為12﹪;As最小,僅為7.0﹪當(dāng)溶劑為l價面心立方金屬時,溶入

2價或

2價以上溶質(zhì)元素時最大溶解度極限對應(yīng)的極限電子濃度為1.36;l價體心立方金屬為溶劑時,此極限值為1.48,而以密排六方金屬為溶劑時,此極限值為1.7598992.4間隙固溶體2.4.1間隙固溶體的概念2.4.2形成間隙固溶體的條件2.4.3間隙固溶體的固溶度100InterstitialsolidsolutionIninterstitialsolidsolutionstheatomsoftheparentorsolventmetalarebiggerthantheatomsofthealloyingorsolutemetal.Inthiscase,thesmalleratomsfitintointersticesi.espacesbetweenthelargeratoms.Thepurpleatomsaresmallenoughtofitintothespacesbetweenthelargersolventatoms.

1011022.4.1間隙固溶體的概念

當(dāng)原子半徑比較小的非金屬元素作為溶質(zhì)溶入金屬或化合物的溶劑中時,這些小的溶質(zhì)原子不占有溶劑晶格的結(jié)點位置,而存在于間隙位置,形成間隙固溶體.

1032.4.2形成間隙固溶體的條件溶劑:大多是過渡族元素溶質(zhì):一般是原子半徑小于0.lnm的一些非金屬元素,即氫0.046、氧0.061、氮0.071、碳0.077、硼0.097等

保證⊿R＞41﹪電負(fù)性差不大1042.4.3間隙固溶體的固溶度固溶度都很小

原因是溶質(zhì)原子存在于間隙位置上引起點陣畸變較大,所以它們不僅不可能填滿全部間隙,而且一般固溶度都很小

γ-Fe:八面體間隙α-Fe:八面體間隙CN填滿實際填滿實際γ-Fe

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