On the mechanisms of two-way memory effect and stress-assisted two-way memory effect in NiTi shape memory alloy

This study aims at understanding the predominant mechanisms responsible for the maximum TWME and SATWME. It was found that partial reverse transformation initiated under constraint condition resulted in the generation of two-step phase transformations. The transformation occurring at higher temperature is attributed to the postponed memory effect of retained martensite. Although this retained martensite causes significant reduction in SATWME, it causes merely insignificant changes in TWME. These changes in memory effects are due to the generation of internal plastic deformation. The critical factor that determines the maximum memory effect therefore is attributable to the favorable dislocations and internal stress field created during martensite pre-deformation and under constrained thermal cycling.