AUSTENITE AND MARTENSITE MICROSTRUCTURES IN SPLAT-COOLED NI-AL

The martensitic transformation in splat-cooled Ni62.5Al37.5 and Ni65Al 35 material is investigated by different transmission electron microsc opy techniques. It was found that the extreme conditions of the rapid quench produce much smaller grains with a higher dislocation density t han in bulk material. The martensite start temperature M-s is also sli ghtly increased, probably due to internal stresses, leading to small m artensite plates inside the Ni62.5Al37.5 B2 grains. The microstructure of completely transformed grains in Ni65Al35 reveals several peculiar features again pointing towards internal stress configurations. (C) 1 998 Elsevier Science Limited. All rights reserved.