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

This work presents some preliminary results relating training treatment, tr aining temperature and the formation of alpha' martensite to the shape reco very effect of stainless shape memory alloys. For the composition tested, t he sample shows some mechanical memory (constant tensile stress at 4% strai n and constant yield stress throughout the training cycles) with a very goo d shape recovery (95% after 4% tensile strain) at a training temperature of 873 K. Its residual strain is related to the generation of perfect disloca tions only. For the sample trained at 723 K, the residual strain could be a ttributed to incomplete reversion of stress-induced epsilon martensite, in part due to the blocking effect of alpha' martensite and also to the genera tion of perfect dislocations. The influence of alpha' martensite on shape r ecovery is relative and is dependent on training temperature, and the prefe rential growth of alpha' martensite is shown to occur for large grain size. (C) 1999 Elsevier Science S.A. All rights reserved.