Timpel, M.; Wanderka, N.; Schlesiger, R.; Yamamoto, T.; Isheim, D.; Schmitz, G.; Matsumura, S.; Banhart, J.: Sr-Al-Si co-segregated regions in eutectic Si phase of Sr-modified Al-10Si alloy. Ultramicroscopy 132 (2013), p. 216-221
10.1016/j.ultramic.2012.10.006

Abstract:
The additionof200ppmstrontiumtoanAl–10wt%Sicastingalloychangesthemorphologyofthe eutecticsiliconphasefromcoarseplate-liketofinefibrousnetworks.Inordertoclarifythis modificationmechanismthelocationofSrwithintheeutecticSiphasehasbeeninvestigatedbya combinationofhigh-resolutionmethods.Whereasthree-dimensionalatomprobetomographyallows us tovisualisethedistributionofSrontheatomicscaleandtoanalyseitslocalenrichment, transmissionelectronmicroscopyyieldsinformationaboutthecrystallographicnatureofsegregated regions.SegregationswithtwokindsofmorphologieswerefoundattheintersectionsofSitwin lamellae:Sr–Al–Sico-segregationsofrod-likemorphologyandAl-richregionsofsphericalmorphology. Both areresponsiblefortheformationofahighdensityofmultipletwinsandpromotetheanisotropic growth oftheeutecticSiphaseinspecificcrystallographicdirectionsduringsolidification.The experimentalfindingsarerelatedtothepreviouslypostulatedmechanismof‘‘impurityinduced twinning’’.