Fe containing phase in Al-Si-Fe alloy Some typical paper on Fe containing phase in Al-Si-Fe alloys. They are useful for the investigation on nucleation and phase transformation.

MaterialsScienceandEngineeringA304–306(2001)

215–219

HeterogeneousnucleationmechanisminAl–Fe–Siamorphousalloys

P.Schumacher ,P.Cizek

DepartmentofMaterials,UniversityofOxford,ParksRoad,OxfordOX13PH,UK

Abstract

Al70Fe13Si17alloysweremelt-spunwithcommercialgrainre neradditionscontainingTiB2andAl3Tiparticles.X-raydiffraction,calorimetryandtransmissionelectronmicroscopyrevealedincompletevitri cation.ThesizeandnumberdensityofAlcrystalsincreasedwithdecreasingquenchrate.Fullcrystallisationledtoformationof -Al9FeSi2andAl.Inas-quenchedsamplesnucleationeventsonTiB2particlesweresurroundedbynanocrystalline -Alparticlesembeddedinamorphousphase.BorideparticleswerecoveredinathinTi-containinglayerandsurroundedbyafeaturelesszonereminiscentofaperitecticreactionandtheyexhibitedanorientationrelationshiptonextneighbourAlparticles.©2001ElsevierScienceB.V.Allrightsreserved.

Keywords:Grainre ner;Al–Fe–Si;Heterogeneousnucleation

1.Introduction

Recentstudies[1–4]http://qufufansheng.commercialgrainre neradditionstoAl,containingAl3TiandTiB2particlesembeddedinanAlma-trix,canbeaddedtoglass-formingAlalloys,whichonrapidcoolingarefrozenintoanamorphousmatrix.Nucleationof -Aloccursabovetheglasstransitiontemperatureafterwhichgrowthofnucleationsitesishaltedandsubsequentelectronmicroscopystudiesreadilyallowidenti cationofnucleationcentres[1,2].Inpreviouswork[1–4] -AlwasnucleatedepitaxiallyonanadsorbedperitecticAl3TilayeronbasalfacesofTiB2particlesembeddedinamorphousAl–Y–Ni–Coalloy.Whiletheobservednucleationmecha-nismwasfoundtobeconsistentwithconventionalcastingpractice[4],theamorphousAl–Y–Ni–Comatrixwassome-whatremovedfromtypicalcompositionsofconventionalAlalloysbasedonAl,FeandSi.Al,FeandSiarefoundindiluteforminmostwroughtAlalloysandinconcentratedformincastingalloys.InwroughtAl–Si–FealloysthehighatomicmobilityinthemeltatthemeltingpointhasbeenpostulatedtoresultintotalconsumptionofanyperitecticAl3Tilayer.Incontrast,inglass-formingalloysthemobil-itycanbeafactorof1016lower[1,4]andobservedperi-tecticlayersappearnottodissolve.ThehighSicontentsinhypo-eutecticcastingalloys(2–12at.%Si)havebeenfoundtohavedetrimentaleffectsongrainre nementofAl[5].Sihasbeensuggestedtoeithereffectthenucleationmecha-nismonAl3Ticoveredboridesbysoluteinteractiontoform

Al3(Ti,Si)orotherreplacementlayerswithlowernucleationpotency,oreffectgrowthrestriction.Si-containingphasessuchas -Al–Fe–Si, -Al–Fe–SiandAl–Ti–SicompoundslimittheamountofSiavailableforgrowthrestriction.Inthiswork,apreviouslydeterminedglass-formingAl70Fe13Si17alloy[6,7]wasdopedwithconventionalgrainre nerad-ditions(containingAl3TiandTiB2)andtheireffectonthenucleationof -Alandintermetallicsisstudiedundervariedquenchingconditions.2.Experimentalmethods

IngotswerepreparedfrompureAl(99.998wt.%),Si(99.999wt.%)andFe(99.98wt.%)togivenomi-nalmatrixcompositionsofAl70Fe13Si17(at.%)totalling{[Al(1 x)Tix]70Fe13Si17}99.88+[TiB2]0.012,x=0.05withgrainre neradditioncontainingAl,TiandBintheformofAl3TiandstableTiB2particles.Additionofgrainre nerwasduringmelt-spinning,sothatthematrixingotcontainedlessAl.Repeatedarc-meltingofsectionedingotswasonawater-cooledcopperhearthinreducedinertatmosphereofAr(200mbar).Theingotsweresectionedto2–3gpor-tionsandmelt-spununderinertHeatmospherewithwheelspeedsof30,40and50ms 1withvaryingejectiontemper-aturesof950,1000and1050±10 C.Lowertemperaturesthan950 Cdidnotresultinsuccessfulejectionbecauseofincreasedviscosity.Typicalribbonswere25–40 minthicknessand2–3mminwidthwhiletheirbrittlenatureresultedinvaryinglengthbetween2and60mm.Thevit-ri cationoftheas-quenchedribbonswasinvestigatedinaDSC(Mettler821E)withheatingratesof20 C/minand

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0921-5093/01/$–seefrontmatter©2001ElsevierScienceB.V.Allrightsreserved.PII:S0921-5093(00)01491-X