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1、MaterialsScienceandEngineeringA454455(2007)252259Analysisofmicrostructureformationingas-atomisedAl12wt.%Sn1wt.%CualloypowderC.J.Kong,P.D.Brown,S.J.Harris,D.G.McCartney∗SchoolofMechanical,MaterialsandManufacturingEngineering,UniversityofNottingham,UniversityPark,NottinghamNG72RD,UKReceived24Augus
2、t2006;receivedinrevisedform3November2006;accepted7November2006AbstractThemicrostructureofgas-atomisedAl12wt.%Sn1wt.%Cualloypowderhasbeeninvestigatedusingscanningandtransmissionelectronmicroscopy.Powderparticlesaboveapproximately8mindiameterexhibitedacellulardendriticsolidificationmorphologycompr
3、ising-AldendritesandinterdendriticSn.Insmallerpowderparticles,withdiameterslessthanapproximately8m,themicrostructurecomprisedan-Almatrixwithadispersionofsub-micronSnparticles.ThesizeofthedispersedSnphasedecreasedwithdecreasingpowdersize(i.e.increasedcoolingrate).Theformationofthisdispersedpha
4、semicrostructureisexplainedbytheexistenceofametastableliquid-phasemiscibilitygapinthesystemsuchthatthereactionL→L1+L2occurredpriortotheonsetofsolidificationinparticlesbelow8minsize.Aheattransferanalysiswasusedtoestimatetheundercoolingforthenucleationof-Alindropletscooledatdifferentrates.Thenucl
5、eationundercoolingpredictedforan8mdiameterdropletwas260Kandthisrepresentsacriticalvaluewhichmustbeexceededtoentertheimmiscibilityregion.Theabovevalueisinreasonableagreementwiththetemperatureofthemetastableimmiscibilityboundary,calculatedfromthermodynamicdata,whichoccursatanundercoolingofapproxi
6、mately280KforAl12wt.%Sn.©2006ElsevierB.V.Allrightsreserved.Keywords:Rapidsolidification;Microstructure;Aluminiumtin;Undercooling;Phaseseparation1.Introductioncontainerlesssolidificationinadroptube,glassfluxing,elec-tromagneticlevitation,meltspinningandelectronbeamsurfaceAnumberofbinaryalloysystems,
7、suchasFeCu[1],possessmelting[315]toachievelargeundercoolingsandrapidsolidifi-aliquiduslineontheirphasediagramthatisnearlyhorizontalcation.Ithasbeenshownthatdropletsofaliquid-phase,L1,canoverasignificantrangeofcompositions.Such