Effect of heat treatment on the microstructure and properties of a Ti₃Al linear friction welding joint

Heat treatment at different temperatures was carried out on a Ti₃Al linear friction welding joint. The characteristics and evolution of the microstructure in the weld zone (WZ) and the thermo-mechanically affected zone (TMAZ) of the Ti₃Al LFWjoint were analyzed. Combined with the heat treatment after welding, the effect of the heat treatment temperature on the joint was discussed. The test results indicated that the linear friction welding (LFW) process can accomplish a reliable connection between Ti₃Al alloys and the joint can avoid defects such asmicrocracks and voids. The weld zone of the as-welded Ti₃Al alloy joint was mainly composed of metastable β phase, while the TMAZ wasmainly composed of deformed α₂ phase andmetastable β phase. After being heat treated at different temperatures, theWZ of the Ti₃Al LFWjoint exhibited a significantly differentmicrostructure. After heat treatment at 700 °C, dot-like structures precipitated and the joint microhardness increased significantly. Subsequently, the joint microhardness decreases with the increase in temperature. Under heat treatment at temperatures above 850 °C, the formed structure was acicular α₂ phase and the joint microhardness after heat treatment was lower than that of the as-welded joint.