Microstructure characteristics and mechanical properties of laser-TIG hybrid welded dissimilar joints of Ti-22Al-27Nb and TA15

Laser-TIG-hybrid-welding (TIG - tungsten inert gas) process was successfully applied to investigate the microstructure and tensile properties of Ti-22Al-27Nb/TA15 dissimilar joints. The HAZ of the arc zone in Ti-22Al-27Nb was characterized by three different regions: single B2, B2+α₂ and B2+α₂+O, while the single B2 phase region was absent in the HAZ of the laser zone. As for the HAZ in TA15 alloy, the microstructure mainly contained acicular α′ martensites near the fusion line and partially remained the lamellar structure near the base metal. The fusion zone consisted of B2 phase due to the relatively high content of β phase stabilizing elements and fast cooling rate during the welding process. The tensile strength of the welds was higher than that of TA15 alloy because of the fully B2 microstructure in the fusion zone, and the fracture preferentially occurred on the base metal of TA15 alloy during the tensile tests at room temperature and 650 °C.