Dissimilar laser welding of NiTi shape memory alloy to NiCr alloy

NiTi shape memory alloy (SMA) offers a wide range of industrial applications due to its shape memory effect and superelastic properties. In this study, a dissimilar joint between NiTi SMA and Ni–20Cr alloy was fabricated, and its microstructural and mechanical properties were analyzed. As a result of the formation of brittle intermetallic compounds (IMC), the tensile characteristics were reduced, and the hardness increased dramatically. Also, the effect of various laser pulse widths on bonding characteristics was examined, and as the pulse width increased, coarser IMCs were formed in the FZ. By performing post-weld heat treatment (PWHT) on the welded samples, the microstructure and mechanical properties of the FZ changed, and the NiTi intermetallic phase was produced. The results revealed that most IMCs generated had the same chemical composition ratio as Ni3Ti and Cr2Ti IMCs. In addition, after PWHT, the plateau region in the stress-strain curves was formed, while in the welded samples without PWHT, the joints failed at low stress and strain before forming the plateau region.