NiTi wires welding using a 500 W pulsed Nd:YAG laser equipment

Abstract

The welding of NiTi shape memory alloys is an issue of highly importance for the generation of dissimilar and quasi-dissimilar architectures. Among the solutions for joining NiTi alloys, the laser welding has numerous advantages, among which: a low energy used in the process, the possibility to focalize the energy in a precise region and a large range of parameters used.The welding of the two NiTi wires with 0,74 mm diameter was performed using a commercially equipment (Nd3 +: YAG type PE-W500II Perfect Laser Co., LTD), leading to joints with an overlap factor of about 50% using the following parameters: 200 A current intensity, 5 ms laser beam pulse duration and 5.7 Hz pulse frequency.The welds obtained were analyzed by optical microscopy to characterize the NiTi memory alloy wires, the appearance of the weld and the compositional differences between the different areas of the joint.The fragile rupture occurred in the marginal area of the spot. It should be noted that the rupture occurred in the heat affected zone (HAZ), but not in the area of the welded joint, being typical for joints made without a protective atmosphere of Ar (inert gas).