A comprehensive insight into the superelasticity measurement of laser welded NiTi shape memory alloys

In this work, superelastic response of laser welded NiTi wires were studied using nanoindentations and cyclic tensile tests. At high power laser condition ~0.4 wt% of Ni content evaporated, which resulted in the formation of the martensite phase due to about 40 °C shift in the Af temperature. This caused in 500 nm residual depth after the cyclic load-unload nanoindentation test and 1.9% residual strain after the cyclic tensile test, both signs of superelasticity deterioration. However, by adopting the possible lowest power laser condition, these parameters became 200 nm and 1%, respectively. By increasing the cyclic tensile test temperature to 60 °C (above Af), similar superelastic responses were achieved due to the elimination of any unfavorable martensite phases inside their fusion zones.