Microstructure development during dissimilar welding: case of laser welding of Ti with Ni involving intermetallic phase formation

Abstract

Development of solidification microstructure in a laser welded Ti/Ni dissimilar binary couple is presented. At the fusion interfaces in both Ti and Ni, growth of the base metal grains into the weld pool is inhibited by the resence of composition gradients in the melt. Ti₂Ni dendrites grow toward the base metal at the Ti fusion interface. In the Ni side, appearance of a nickel solid solution phase is followed by layers of Ni₃Ti, Ni₃Ti + NiTi, eutectic, and NiTi. NiTi dendrites and Ti₂Ni constitute the microstructure in the middle of the weld. Isolated titanium dendrites are observed throughout the weld, but their preferential occurrence toward the top surface of the weld is more prominent. Results are rationalised on the basis of interplay of the transport processes in the weld with the thermodynamics of the Ti-Ni system.