Effect of Thermomechanical Cycling on the Recovery Characteristic of Tinife Shape Memory Alloy

Abstract

Pre-strain ratios and thermomechanical cycling (TMC) times have significant effects on the recovery of the characteristics of TiNiFe shape memory alloy. In this study, the microstructure, recovery properties, transformation temperatures, residual stress and misorientations of cold-rolled TiNiFe pipes with different pre-strain ratios and different thermomechanical cycling times were analyzed. The results show that the increase of pre-strain ratio caused a severe reorientation of martensite at liquid nitrogen temperature and leads to the stabilization of martensite, which resulting in the increasing of elastic strain, plastic strain, recovery strain, residual strain and the reverse transformation temperature of the TiNiFe alloy during deformation and recovery process. Additionally, the maximum fully recoverable strain of TiNiFe alloy is 8%. When the pre-strain ratio increases, with an increase in TMC times, the reorientation of martensite and the irreversible slip plastic deformation become severe, and the plastic deformation accumulates continuously. At the same time, due to the multiplication and movement of dislocations during the TMC process, the deformation energy is accumulated, causing an increase in various strains of TiNiFe alloy after TMC process and the decreases of reverse martensite transformation temperature.

Keywords: TiNiFe alloy, Shape memory alloy, Thermomechanical treatment, phase transformation