Effects of Grain Size Gradient on Deformation Behavior of Superelastic NiTi Plate

Abstract

The superelastic NiTi shape memory alloy with grain size distributed from 20 nm to 175 nm along the gauge length is fabricated by cold rolling and gradient heat treatment. This study investigated the effects of grain size gradient on deformation behavior of the NiTi plate under strain controlled quasi-static loading-unloading. Experimental results show that when the grain size decreased from 175 nm to 35 nm, the phase transformation stress increased from 380 MPa to 509 MPa, and the stress slope increased from 0.6GPa to 14.15GPa. With a simple phenomenological model, we have simulated the stress-strain responses and demonstrated the mechanism of the deformation behaviors of the grain size gradient superelastic NiTi plate. The study indicates that the particular behavior of the plate is due to grain size effects of coexisting grain size gradient.