Effect of Annealing on Strain-Temperature Response under Constant Tensile Stress in Cold-Worked NiTi Thin Wire

The present paper aims to understand the influence of annealing on the strain-temperature response of a cold-worked NiTi wire under constant tensile stress. It was found that transformation behavior, stress-strain relationship, and strain-temperature response of the cold-worked NiTi wire are strongly affected by the annealing temperature. Large martensitic strains can be reached even though the applied stress is below the plateau stress of the martensite phase. At all stress levels transformation strain increases with increasing annealing temperature in the range of 350∘–450∘C and decreases with increasing annealing temperature in the range of 450∘–650∘C. The martensitic strain at lower stress levels exhibits the same tendency. At higher stress levels the martensitic strain increases with increasing annealing temperature.