THE INFLUENCE OF DISLOCATION ARRANGEMENTS IN AUSTENITE ON THE COURSE OF DIFFUSIONLESS TRANSFORMATION IN CU-BASED SHAPE-MEMORY ALLOYS

The transformation behaviour of shape memory alloys is influenced by l attice defects. Due to these defects the characteristic temperatures a nd mode of transformation can be varied. To examine the effect of disl ocations on the transformation behaviour, CuZnAl and CuAlNi alloys wer e deformed plastically by different amounts in the stable austenitic a nd in the martensitic state. The induced dislocations can be arranged as random dislocation forests, dislocation groupings, subgrain boundar ies, tangles and cell walls. LM and TEM investigations connected with DSC measurements were conducted to characterize changes in microstruct ure and functional properties. A critical amount of plastic deformatio n promotes a premartensitic solid-solid state reaction even in Cn-base d SMA and retards or inhibits the martensitic transformation.