Study on microstructure and microhardness of linear friction welded joints of Ti-22Al-27Nb alloy

In this paper, the Ti-22Al-27Nb based alloy was welded by linear friction welding (LFW), and then subjected to post-weld heat treatment. The microstructure and the microhardness of the linear friction welded joints were investigated. The results showed that the sound joints free of defects can be obtained by using LFW method. As welded condition, the weld zone is mainly composed of metastable B2 phase. In thermo-mechanically affected zone, equiaxial α₂ occurred in this zone and the acicular O phase nearly disappeared. After heat treatment, the lath O phase and acicular O phase precipitated at weld zone, the thermo-mechanically affected zone is a two-phase region with uniform distribution of O phase. The microhardness of base material is about 300 HV, the microhardness increases with approaching to weld center, which maximum microhardness is 354 HV. After heat treatment, the microhardness of the weld center increased sharply due to precipitation of lath O and acicular O phase.