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1、jo.......CRYSTALGROWTHELSEVIERJournalofCrystalGrowth173(1997)182188InterfaceinstabilitiesonsolidifyingglobuliticparticlesM.Rettenmayr*,O.PornpeMaterialsScienceDepartment,TechnicalUniversi~Darmstadt,Petersenstrasse30,D-64287Darmstadt,GermanyReceived15June1996;accepted18Septemb
2、er1996AbstractA1-6.8wt%Cusampleswereheldinthemushyzoneatafractionofsolidof50%for5000sandthencooled/quenchedwithcoolingratesbetween0.02and160K/s.Thecoarse~t-A1particlesformedduringtheisothermalholdingperiodgrowwithanunstableinterfaceduringthequenchingprocess.Finecellsanddendri
3、tesdeveloponthesurfaceoftheprimaryparticles.Atlowcoolingrates,ifthesolutalboundarylayersofneighbouredparticlesoverlap,nosolutalinstabilitiesareseen.Measurementsoftheinterceptlengthinthequenchedformerliquidandcorrelationthereofwiththesolutalboundarylayershowagoodqualitativeagr
4、eementfortheconditionsofcellformationand"stable"growth,respectively.Thereisalsoagoodquantitativeagreementbetweenmeasuredandcalculatedcellspacings.1.Introductiontheparticles,andequiaxeddendritesgrow.Whentheeutectictemperatureisreached,theshapeoftheUsingsubsequentstepsofcooling
5、andisother-cellsanddendritesisretainedtothefullysolidifiedmalholding,avarietyofmicrostructurescanbestate,sincethefirstthinlayerofeutecticcoveringproducedinmetalalloys.Duringisothermalhold-the~crystalsbringscompetitivegrowthandingbetweenliquidusandsolidustemperature,ancoarseni
6、ngofdendritearmstoanend.Theinitiallydendriticmicrostructurereducesitssurfacecell/dendritearmspacingisdeterminedbyanin-energybyachangeofshapetowardssphericalitialspacing2oofthedevelopinginstabilitiesandparticlesandbycoarsening.Iftheheatextractionsubsequentcoarsening.Theinstabi
7、litiescandevel-duringfurthercoolingisthroughthemelt,theopduetothethermalorsolutalfieldinfrontoftheinterfaceofthegrowingparticlesisinherentlyun-movinginterface.Foralloys,generally,solutalstable.Afterthebuilt-upofaconcentrationorcells/dendritesareexpected.thermalgradient,cells(
8、ordendrites)developontheTheconditionsunderwhichtheinterfaceofthesurf
