Thermomechanical training and the shape recovery characteristics of NiTi alloys

Thermomechanical training is an important process to develop a two-way memory effect (TWME) in shape memory alloys. The present study has been dedicated to understand the mechanisms responsible for the TWME by examining its correlation with a stress-assisted two-way memory effect (SATWME). It was observed that imposing partial transformation between As and Af temperatures during training induces a two-step transformation. The appearance of two-step transformation was observed to be a one-time only phenomenon. The magnitudes of SATWME and TWME were both found to decrease with partial transformation, though their decreasing trend varied according to different cyclic conditions. The internal stress developed by the partial transformation was ineffective in promoting the SATWME and TWME. On the contrary, the internal stress developed by the full transformation during training is favorable to the development of SATWME and TWME.