Effect of heat treatment on the two-way recovery stress of tube-shaped NiTi

Abstract

The effect of annealing temperatures on the thermomechanical behavior of NiTi in terms of transformation temperatures, mechanical properties, two-way shape memory strain, and two-way recovery stress was investigated experimentally to develop a NiTi tubular actuator with high two-way recovery force. Five tubular specimens were used to obtain the two-way shape memory strain and two-way recovery stress by varying heat treatment conditions. Annealing heat-treated temperatures were 400 degrees C, 500 degrees C, 600 degrees C, 700 degrees C, and 800 degrees C. A two-way shape memory effect was introduced in the shape memory alloy tube by thermomechanical treatment after annealing heat treatment. According to the results, the two-way strain induced by shape memory cycling was independent of the annealing temperature. However, the two-way recovery stress generated by the two-way strain depended on the annealing temperature, even though the values of the two-way strain were similar in all specimens. Considering all heat treatment results, we concluded that the optimum annealing temperature to acquire two-way recovery stress and two-way strain for an actuator is 600 degrees C.