Intergrowth Bonding Mechanism and Mechanical Property of Linear Friction Welded Dissimilar Near-Alpha to Near-Beta Titanium Alloy Joint

Linear friction welding (LFW) of dissimilar near-alpha TA19 (Ti–6Al–2Mo–4Zr–2Sn) to near-beta TB2 (Ti–5Mo–5V–8Cr–3Al) titanium alloys is conducted with two preset axial shortenings to further explore the bonding mechanism of LFW. The microstructure evolution of the joints is analyzed by using an optical microscope, scanning electron microscope, and transmission electron microscope. The tensile properties and Vickers hardness of the joints are tested. The results show that there are obvious differences in the macro- and microstructure characteristics on both TA19 and TB2 sides of the joint resulting from the different thermomechanical coupling effects, and different dynamic recovery/recrystallization behaviors due to their differences in high-temperature strength, thermal conductivity, and alloying elements. It is found that for a sound joint (larger axial shortening), a large number of high-angle grain boundaries are formed in the weld zone (WZ) on the TA19 side through continuous dynamic recrystallization, and a large number of low-angle grain boundaries are obtained in the WZ on the TB2 side via dynamic recovery. The mutual migration of grain boundaries on both sides of the weldline leads to the formation of intergrowth grains, making the dissimilar TA19 to TB2 joint a reliable bonding.