High power CW YAG laser weldability of dissimilar Ti to Ni metal plates through beam shift

Incompatibilities of thermo-physical-mechanical as well as metallurgic properties between dissimilar Ti and Ni metals present technical challenges to their fusion joining. In this manuscript, using a high power continuous wave (CW) YAG laser, a direct butt welding of Ti and Ni plates was performed with a relatively large beam offset from the contact interface between two base metals (BMs) toward either side of the BMs. As a result, a large amount of rapidly solidified non-equilibrium solid solution occurred in the main fusion zone (FZ); while the total amount of prior intermetallic compounds (IMCs) such as Ti₂Ni, Ni₃Ti and NiTi significantly decreased, most of which were primarily located as a band (less than 200 μm wide) along one of the fusion interfaces with the BMs. When the laser beam was shifted 0.5 mm toward the Ni side, the toughness of the FZ was sufficiently improved, leading to a crack-free joint. In this study, the microstructures, chemical compositions, and microhardness in the laser-welds thus obtained were examined to learn the influences of beam offset on laser weldability of Ti to Ni metals.