Influence of the microstructure on the stability of the intrinsic two-way shape memory effect

This work presents a study of the development of the two-way shape memory effect (TWSME) and its degradation due to working cycles. An intrinsic TWSME was induced in wire specimens of two near equiatomic NiTi alloys by thermomechanical training. The development of the effect was analyzed and discussed with respect to the different microstructures obtained by preliminary heat-treatment of the samples. The investigations show that training of cold worked specimens results in a smaller extension of the TWSME, but the effect remains more stable during service cycles compared to annealed samples. Precipitates have a strong negative effect on the trainability of the alloy. They considerably impede the evolution of the recoverable strain, thus limiting the obtainable magnitude of the two-way strain.