Superelastic behavior of aged and thermomechanical treated NiTi alloy at Af + 10 °C

The phase transformation in NiTi shape memory alloys is very sensitive to aging and thermomechanical treatment (cold work and annealing). In this research, a Ni-rich alloy has been cold-rolled and then subjected to various annealing treatments and also aging treatments at different temperatures and times. To investigate the superelastic behavior, mechanical testing was carried out at Af + 10 °C to eliminate the effect of testing temperature on the superelasticity parameters including loading/unloading plateau and mechanical hysteresis. The effect of dislocations and precipitates resulted from thermomechanical and aging treatments on the transformation behavior was studied by Differential Scanning Calorimetry (DSC) and three point bending (TPB) tests. The results showed that these treatments are effective on the thermal and mechanical-induced phase transformation characteristics. Transformation temperatures increase and loading/unloading plateau and thermal and mechanical hystereses decrease by increasing aging and annealing time. Increasing of aging and annealing temperatures results in decreasing of loading/unloading plateau and thermal and mechanical hysteresis.