Micro-resistance welding of NiTi shape memory alloy wire and MP35N wire

The micro-resistance welding between NiTi shape memory alloy and Co-35Ni-20Cr-10Mo alloy (MP35N) wires was investigated to gage the feasibility of their future applications. Welding current and electrode force significantly affected the joint breaking force. The highest joint breaking force (0.99 kgf) at the optimized welding parameter (0.51 kA, 7.500 kg) was accomplished by maximizing the solid-state bonded area and minimizing the heat-affected zone (HAZ). This highest joint breaking force was higher than that of the micro-resistance welded NiTi wire joint reported in previous studies. Furthermore, the cyclic tensile test revealed that the accumulated residual strain of NiTi wire was reduced after welding. This could be attributed to the reduction in the dislocation density through grain growth in the HAZ of NiTi wire during the welding process.