The Effect of Annealing and Cold-drawing on the Super-elasticity of the Ni-Ti Shape Memory Alloy Wire

Abstract

Annealing combined with cold-drawing are the necessary method in the processing of Ni-Ti shape memory alloy thin wires. In this paper, the annealing temperature scan of 450~800?, time scan of 20min~3h and the cold-drawing amount of 6.9%~39% were chosen, and their effects on the thermo and mechanical performance of the Ni-50.5a.t.%Ti alloy wires have been studied. The DSC and tensile-recovery tests were adopted to obtain the phase transformation temperatures and mechanical hysteresis of the Ni-Ti SMA wires with different treatment conditions. The results show that the phase transition temperature of Ni-Ti wire can be changed by varying the annealing temperature and time; cold-drawing deformation and subsequent annealing have a great influence on the super-elasticity. Meanwhile, the surface oxide film and the flake cracks were obtained by SEM scanning. To obtain the best super-elasticity with the maximum cold working amount of 39%, the process with 39% cold drawing amount, 600 ? and 20 min annealing is shown to be effective.