Laser Welding of Ti-Ni Type Shape Memory Alloy

Welding and Joining of NiTi Shape Memory Alloys: A Review

“…A two-stage shape memory effect, which is different from the two-way shape memory effect, was observed [126] in welds of two NiTi sheets with different compositions, with full recovery of the imposed deformation on the joint. As the base materials had different transformation temperatures, it was expected that the FZ had a transformation temperature in between them.…”

“…The shape memory effect on laser welded NiTi was reported in early studies [125,126]. Full recovery of the imposed strain was achieved when the samples were heated to the austenitic phase.…”

“…Early laser welding studies on NiTi shape memory alloys were performed using CO ?2 lasers [31,[125][126][127] while, nowadays, the primary choice for these studies are the infrared lasers, such as Nd:YAG [128][129][130][131]145,165,166] and fibre lasers [132][133][134] due to their low wavelength and increased material absorptivity and, thus, narrow welds [38,135].…”

“…In the former the functional properties of the material suffer a degradation during cyclic solicitation, while the latter the material fails, during high cyclic loads like any other engineering material. Several studies report the cycling behaviour of NiTi welds [31,125,126,132,137,140,144,166]. However, a significant disparity in the reported experiments is observed.…”

“…Some interesting properties presented by similar NiTi joints can be used in the future for sensors or actuators. In particular, when joining NiTi with different compositions [126,156], the shape memory effect of the welds can be depicted in two steps, as the different compositions of the base materials give raise to different transformation temperatures. The distinct shape memory effect presented by the thermal affected regions when compared to the original base material [168] may also be used for such applications.…”