The effect of Nd:YAG laser pulse duration and post-weld heat treatment on the microstructure and mechanical properties of laser-welded NiTi shape memory alloy

Abstract

The heat input is the most critical factor in pulsed Nd:YAG laser welding and affects the microstructure and mechanical behavior of the welded alloys. NiTi alloy has been used for various applications such as medical equipment and MEMS due to its unique shape memory effect, superelasticity, and excellent corrosion and fatigue performance. This research investigated the effect of heat input and post-weld heat treatment (PWHT) on the microstructure and mechanical properties of similar NiTi shape memory wires joints. For this purpose, NiTi wires were welded with pulse widths of 5, 8, and 11 ms, and then, heat treatment was performed. Microstructures of the welded alloys were examined using optical and electron microscopes and chemical composition was analyzed with an EDS analysis system. The mechanical properties were evaluated using tensile and microhardness tests. A desirable NiTi SMA joint was achieved by Nd:YAG laser, and the properties were improved by following post weld heat treatment.Investigations showed that microstructure and mechanical properties were changed by increasing the heat input. After applying PWHT due to recrystallization and the creation of new phases in the weld zone, the final strength of the joints increased up to 80%, and the behavior of the plateau region became similar to shape memory behavior in the NiTi alloy.