Superelastic cycling behaviour of flanged NiTi pin fabricated by laser rod end melting and immediate flange processing

A process chain consisting of laser rod end melting with immediate flange processing enables the fabrication of a component connector for NiTi alloys via form-fit joining. In this process, a laser beam melts the end of a NiTi wire into a melt droplet, which is immediately reshaped to a flange, connected to the remaining wire as a flanged pin. Because cyclic loading of NiTi alloys is associated with functional and structural fatigue, it is important to understand the mechanism determining both types of fatigue of the flanged pin. Thus, the effects of process parameters, wire diameter and post heat treatment on the tensile properties, residual strain and low-cycle fatigue life was systematically investigated. Despite the different process parameters, the flanged pins with similar tensile properties exhibited different residual strain and fatigue lives. In addition, the flanged pin made of a thinner wire showed lower residual strain and a longer low-cycle fatigue life. However, the post heat treatment of the flanged pin contributed to no apparent improvement in low-cycle fatigue life. This study reveals the mechanism determining the functional and structural fatigue of the flanged pin under superelastic cycling.