The Mechanism of Thermomechanical Training of a Newly Developed Fe-Mn-Si-Cr-Cu Shape Memory Alloy

Abstract
Thermomechanical training was carried out on a newly developed Fe-20Mn-6Si-7Cr-1Cu shape memory alloy. It was observed that the effectiveness of thermomechanical training largely depends on the recovery annealing temperature and the pre-strain during training. Based on the analysis of the changes in critical stress for martensite formation, the critical stress for slip deformation, the phase transformation temperatures and microstructural development during training, it was concluded that the mechanism of thermomechanical training is based on the following two factors : (1) lowering of the critical stress for martensite formation, making stress induced γ→ε transformation easier ; and (2) decreasing the Af temperature and refining the ε martensite structure, thus reducing the energy barrier for the ε→γ reverse transformation. The optimum thermomechanical training conditions have been determined for the alloy studied.