Microstructural evolution of a TC11 titanium alloy during linear friction welding

Linear friction welded titanium alloy microstructures were investigated to understand the microstructural evolution in the joints. The results show that extrusion of material at the rubbing interface occurred after complete transformation of alpha to beta phase. Finer prior-beta grains were obtained in the flash as compared to the parent material due to dynamic recrystallization. Metallographic examination revealed that two different structures were existed in the joints, i.e., thermomechanically affected zone developing at the edge of joint and weld appearing in the central portion of joint. Although no dynamic recrystallization was observed in the thermomechanically affected zone, the phase transformation would occur concurrently with material deformation during welding. In contrast, dynamic recrystallization had occurred in the weld. Effect of welding parameter on the microstructure was investigated by changing amplitude of oscillation (1.56-2.03 mm). Some defects such as kiss bonding and porosity occurred in the joint at relatively low amplitude of oscillation. Therefore, relatively high amplitude of oscillation is more preferable for obtaining a fully bonded joint.