| Abstract Scope |
NiTi alloys with a composition of nearly equal atomic concentrations of Ni and Ti exhibit unique properties such as excellent shape memory effect, superelasticity, and biocompatibility. Owing to these properties, NiTi alloys are used in biomedical products such as stents, catheters, and guidewires. These biomedical products require visibility under X-ray irradiation because it is necessary to identify their positions in the human body during surgery. Therefore, PtIr alloys with excellent X-ray visibility sometimes join NiTi alloys as markers. Although laser microwelding is a useful welding technique for joining NiTi and PtIr alloys, brittle intermetallic compounds formed in the fusion zone (FZ) could degrade the joint strength. The influence of the composition of the FZ on intermetallic compound (IMC) formation and the effect of intermetallic compounds on the mechanical properties of the NiTi-PtIr welds remain unclear. The objective of this study was to clarify the effect of IMC formation on the mechanical properties of butt welded Ni-49.8 at.% Ti and Pt-10.0 at.% Ir alloy wires in the diameter of 400 μm. As a technique to control IMC formation, laser offset was applied to butt NiTi and PtIr alloy wires to change the composition of the FZ. Laser offset on the NiTi wire side significantly enhanced joint breaking stress and joint breaking strain. In the absence of laser offset, brittle M3Ti (M = Ni, Pt, Ir) formed in the FZ due to the dissolution of Pt and Ir into the FZ, leading to high crack susceptibility. On the other hand, laser offset to the NiTi side suppressed M3Ti formation by mitigating the dilution of Pt and Ir into the FZ. Laser microwelding with laser offset on the NiTi side should be a promising technique to enhance the strength and ductility of NiTi and PtIr welds. |