Study on laser welding of a Ti-22Al-25Nb alloy: Microstructural evolution and high temperature brittle behavior

Laser welding of a Ti-22Al-25Nb (at.%) alloy was successfully performed in order to investigate the microstructure-property relationship of the welded joints. Numerical simulation of the laser welding process was employed for explaining the microstructural evolution in the fusion zone and the heat affected zone. Following room temperature tensile testing, the failure occurred in the base metal, while at high temperature (650 °C) the failure occurred in the fusion zone. The fracture surface of laser welded joints was examined, revealing features of a brittle fracture at 650 °C. Confocal laser scanning microscopy analysis showed that the grain boundaries became coarser, as the holding time at 650 °C was increased, while stress concentrations were observed at the grain boundaries. Further TEM analysis showed that the nucleation and growth of the O phase were responsible for the brittle behavior during the high temperature tensile testing of the joints.