Effects of pseudoelastic cycling under different temperatures on physical and mechanical properties of a NiTi alloy

The effects of pseudoelastic cycling under different temperatures on physical and mechanical properties of a NiTi superelastic wire were investigated by uniaxial tensile testing. The samples were cyclically deformed up to 6% strain under several test temperatures above the austenite finish temperature (Af). In order to approach a cyclic saturation level, number of cycles was established as 20. The temperature at which mechanical cycling was performed played a strong role on residual strain, dissipated energy and also on the critical stress to induce martensite, being consistent with the Clausius-Clapeyron relationship. It was found that an increase in test temperature resulted in more significant changes in the alloy’s functional behavior, but cyclic stability tended to be reached within fewer cycles. X-ray diffraction results showed that no martensite was stabilized at any condition and that austenite diffraction peaks intensities increased with test temperature, which was attributed to stress relaxation. Tensile tests until rupture and three point bending tests revealed that the mechanical response of the specimens cycled at higher temperatures and as received were fairly similar, and that specimens cycled at lower temperatures exhibited a slightly higher flexibility.