Microstructure and mechanical properties of continuous drive friction welded Ti2AlNb alloy under different rotational rates

Ti2AlNb-based alloy was joined in a continuous drive friction welding machine under different rotational rates (500, 1000 and 1500 r/min). The microstructure and mechanical properties of the joints were investigated. It is shown that the weld zone (WZ) is fully composed of recrystallized B2 phase, and the grain size decreases with increasing rotational rate. The thermo-mechanically affected zone (TMAZ) suffers severe deformation during welding, due to which most of original precipitation phase is dissolved and streamlines are present. In the heat affected zone (HAZ), only the fine O phase is dissolved. The as-welded joint produced using 1000 r/min has the best mechanical properties, whose strength and elongation are both close to those of the base metal, while the as-welded joint obtained using 500 r/min exhibits the worst mechanical properties. Post-weld annealing treatment annihilates the deformation microstructure and fine O phase precipitates in the joints, consequently improving the mechanical properties significantly. Decomposed alpha 2 phase is a weakness for the mechanical performance of the joint since microcracks are apt to form in it in the tensile test.