Abnormal superelastic cyclic behavior and stress-induced martensitic transformation mechanism of NiTi alloy with R phase

Abstract

In this work, an abnormal phenomenon of the superelastic cycle in NiTi alloy with R phase is reported. The phase transformation of the 500°C-annealed-sample is B2-R-B19'. During the first superelastic cycle, the critical stress of stress-induced martensitic transformation (SIMT) is reduced to 305.5 MPa and the phase transition plateau is shortened. With the loading process, the transformation of R–B19′ and the elastic deformation of the B19′ occur. With the unloading process, martensite reversal transformation occurs and the high-density dislocation zone and residual martensite are formed. During the superelastic cycle, the R phase is consumed. The increase of irreversible residual martensite and crystal defects leads to the deterioration of superelasticity.