Intermetallics14(2006)444–449www.elsevier.com/locate/intermetEBSDcharacterisationofmassivegnucleationandgrowthinaTiAl-basedalloyS.R.Dey,E.Bouzy,A.Hazotte*Laboratoired’EtudedesTexturesetApplicationauxMate´riaux,UMRCNRS7078,IleduSaulcy,57045MetzCedex1,FranceReceived1March2005;receivedinrevisedform18July2005;accepted15August2005Availableonline10October2005AbstractElectronbackscattereddiffraction(EBSD)hasbeencarriedouttoobtainlargeorientationmapsofmassiveg(gm)structuresinaTi–46.8Al–1.7Cr–1.8Nb(at.%)alloy.gmgrainspresentingaBlackburnorientationrelationshipwithoneofthetwoparentagrainsweredetectedalongseverala/aboundaries.Accordingtopreviousstudies,theywereidentifiedasoriginalgmnuclei.Alongagivena/agrainboundary,gmnucleiinrelationwithoneagrainwerealwaysshowntobedominantwithrespecttotheother.Moreover,whiletwotwinvariantsareexpectedforthisgmnucleustype,ourstudypointedoutthepredominanceofoneofthetwotwins.Theseclearselectionphenomenaareanalysedintermsoffavourableorientationrelationshipbetweenthegrainboundaryplaneandthehabitplaneofgmnucleus.AnoriginalanalysisofEBSDmapspointedoutthatalargemajorityofthegmgrainspresentinthemicrostructurecanbegroupedinaslarge‘twin-domains’,inheritedfromthegrowthoftheseinitiallyfavouredBlackburnorientationrelated(OR)gmnuclei,throughamechanismofsuccessivetwinnings.ThisgrowthfirstlyoccursintheagrainhavingnoBlackburnorientationrelationshipwiththeoriginalnucleus,butlatergenerationsofgmtwinscanfurtherre-enterintotheoriginalparentagraininBlackburnorientationrelationship.AlthoughsomemisorientedorunfavourableBlackburnORgmnucleihavealsobeendetectedclosetothegrainboundaries,theywerealwaysfoundtobedormantwithrespecttofurthergrowth.Dependinguponthedescriptionongmgrains,amechanismoftheirgerminationandgrowthisproposed.q2005ElsevierLtd.Allrightsreserved.Keywords:A.Titaniumaluminides;B.Phasetransformation;F.Scanningelectronmicroscopy;B.Twinning1.IntroductionwithoneneighbouringagrainandafewgmgrainswhicharemisorientedfromBlackburnOR.On