Microstructure and mechanical behaviors of TiNiNb wide hysteresis shape memory alloy wire argon arc welding joint

The microstructure and mechanical behaviors of TiNiNb wide hysteresis shape memory alloy (SMA) argon arc welding joint have been systematically investigated in the present paper. The experimental results show that the microstructure of the welding point can be changed to the fine and uniform equiaxed grains by the proper annealing treatment, resulting in the excellent mechanical behaviors of the welding joint. At the ambient temperature, the tensile strength and elongation of the welding joint after proper annealing are relatively high. For the welding joint without annealing, the fraction occurs in the fusion area of the welding point during the tensile process, and obvious cleavage steps have been observed in the fracture, implying that the break is brittle. Whereas for the welding joint after annealing, the crack occurs in the heat affected zone (HAZ), and dimples are observed in the fracture, suggesting that the fracture is ductile. (Ti, Nb)₂Ni particles are found at the bottom of the dimples. And obvious mico-cracks exist in both the interior of the particles and the interface between the (Ti, Nb)₂Ni particle and the matrix. The maximum recoverable strain of the TiNiNb SMA wire with welding joint after annealing is about 5%, indicating that the welding point remains some shape memory effect.