Micro-resistance butt welding of NiTi shape memory alloy to 304 stainless steel micro-wires: Micro-structure evolution and inter-metallic compounds formation mechanisms

Joining NiTi shape memory alloy and 304 stainless steel (SS) presents significant technical challenges, and studies on micro-resistance butt welding (MRBW) of such dissimilar materials are extremely scarce. This work uncovers the nanoscale micro-structure evolution and inter-metallic compounds (IMCs) formation mechanism of NiTi to 304 SS micro-wire joints with a diameter of 0.45 mm during MRBW. Atomic diffusion of Fe and Ni promotes the formation of Fe 2 Ti and Ni 3 Ti phases, which determines the thickness, morphology, and distribution of the interfacial IMC layer. Benefiting from the high-performance Ni 3 Ti phase, the joint fabricated at a welding current of 20 A exhibits the optimal comprehensive performance, with a tensile strength of up to 446 MPa and an elongation of 1.5%.