Relationship between thermomechanical treatment, microstructure and α′ martensite in stainless Fe-based shape memory alloys

This work presents some preliminary results relating training treatment, training temperature and the formation of α′ martensite to the shape recovery effect of stainless shape memory alloys. For the composition tested, the sample shows some mechanical memory (constant tensile stress at 4% strain and constant yield stress throughout the training cycles) with a very good shape recovery (95% after 4% tensile strain) at a training temperature of 873 K. Its residual strain is related to the generation of perfect dislocations only. For the sample trained at 723 K, the residual strain could be attributed to incomplete reversion of stress-induced ε martensite, in part due to the blocking effect of α′ martensite and also to the generation of perfect dislocations. The influence of α′ martensite on shape recovery is relative and is dependent on training temperature, and the preferential growth of α′ martensite is shown to occur for large grain size.