Effect of Laser Welding Preset Rare Earth on the Microstructure and Composition of the Joint of TiNi Shape Memory Alloy

The laser welding preset rare earth for Ti-Ni50.9 at% shape memory alloy was conducted by using Nd-YAG continuous laser-welding machine, in which Ti-50.9at% Ni alloy was prepared by melting process. The microstructure and composition of the weld joint with rare earth were investigated through optical microscopy, scanning electron microscopy, energy spectrum analysis, X-ray diffraction analysis. The results show that the rare-earth element in the weld joint was uniformly distributed without segregated zone. Rare earth with white and fine dispersion grains was distributed in the grain boundary, sub-boundary and internal of sub-crystal cell. The macrostructure of the weld with rare earth is approximately identical to the weld without rare earth. Crystal grain in the weld with rare earth is refined, and the grain boundary, sub-boundary and the directionality of columned crystals are weakened. Adding rare earth elements can improve the strength and toughness of the welded joint of the TiNi alloy.