Microstructure and properties of linear friction welded joint of hyperoxia TC4/TC17 dissimilar titanium alloys

The linear friction welding test was carried out on the hyperoxic TC4/TC17 dissimilar titanium alloys, the analysis of the microstructure evolution of different areas of joint, the diffusion behavior of the alloying elements at the weld line interface and the properties of joint were analyzed. As shown in the results of the test, the phase transformation and dynamic recrystallization occurred in the weld zone during the process of linear friction welding, and eventually forming fine equiaxed grains. The needle-shaped martensite is formed in the weld zone of the hyperoxic TC4 side, while the TC17 side is mainly composed of the metastable β phase. The grains in both sides of the thermos-mechanically affected zone are broken, and elongated along the oscillation direction. During the cooling process of welding, the diffusion behavior of alloy elements appeared near the weld line, and the diffusion area is narrow. The micro-hardness at the center of the weld is up to 420 HV, while decreased gradually as approaching to the base material in the side of TC4. On the contrary micro-hardness of the TC17 side increased rapidly as moving away from the weld center. The tensile test results showed that the tensile strength of the joint is equal to that of the hyperoxic TC4 parent.