Martensitic transformations and microstructures in splat-cooled Ni-Al

The martensitic transformation in splat-cooled Ni-37.5at.%Al and Ni-35at.%A l material is investigated by different transmission electron microscopy (T EM) techniques. It was found that the extreme conditions of the rapid quenc h produce much smaller grains with a higher dislocation density than in bul k material. The martensite start temperature M-s is also increased slightly , probably due to internal stresses, leading to small martensite plates oft en grouped into self-accommodating configurations inside the Ni-37.5at.%Al B2 grains. The 3R martensite microstructure of completely transformed grain s in Ni-35at.%Al reveals several peculiar features again pointing towards i nternal stress configurations. Among these are stepped martensite-martensit e interfaces within a former B2 grain, alternating sequences of martensite microtwin stackings on both sides of a grain boundary between former B2 gra ins and small arrowhead configurations with a 14M-like stacking observed at such grain boundaries. (C) 1999 Elsevier Science S.A. All rights reserved.