Microstructural evolution and mechanical properties of linear friction welded Ti₂AlNb joint during solution and aging treatment

Linear friction welded joints of Ti₂AlNb-based alloy were subjected to different solution and aging treatments. Relationships among solution and aging conditions, microstructural evolution and mechanical properties were investigated. The results indicate that the microstructures are very sensitive to solution conditions. In weld zone, the lath O precipitates at the grain boundaries when the joint is solution treated in O+B2 phase region, while the formation of lath α₂ phase occurs in α₂+B2+O phase region. In thermo-mechanically affected zone (TMAZ), aggregation of O phase and rim O phase resulted from further decomposition of α₂ phase can be found during solution treatment. And after aging treatment, both weld zone and TMAZ are comprised of secondary acicular O phase within B2 grains. Solution and aging treatments have significantly enhanced the microhardness of weld zone due to the precipitation hardening of O phase and refined grain strengthening. After aging treatment, the tensile strength of the joints is further improved because of precipitation of secondary O phase, whereas, elongation is reduced due to the suppression of the hard deformation modes in fine acicular microstructures.