Abstract:The microstructure and elevated temperature tensile properties of Ti₂AlNb/TC18 dissimilar alloy welded joints were investigated by vacuum electron beam welding. The results show that, as the welding processing parameters are adopted properly, the fine acicular α phases are distributed homogenously on the HAZ of the TC18 alloy side. β grain boundary of the weld is obvious, and the fine α phase and α₂ phase are distributed on the β grain boundary. Moreover, the HAZ on the Ti₂AlNb alloy side and the weld are separated obviously, and the β grains are coarsened. Furthermore, the welding processing parameters have little effect on the elevated temperature plasticity of the Ti₂AlNb/TC18 alloy, but they have an obvious influence on its elevated temperature strength. When the welding speed is the same, the elevated temperature tensile strength of welding current of 28 mA is the highest (807 MPa). As the welding current is the same, the elevated temperature tensile strength of welding speed of 6 mm/s is the highest (813 MPa). The reason is that the microstructure of the weld is relatively fine, which leads to the increase of the grain boundary area and the obstruction from the dislocation slip. Therefore, the strength of the joint is improved. When the welding parameters are 28 mA and 6 mm/s, the tensile fracture necking is more obvious, and the dimple is larger and more uniform. All of these are demonstrated that the elevated temperature tensile properties of Ti₂AlNb/TC18 prepared by the welding parameters are better, which is related to the narrow width of the interface and the fine microstructure as well as its uniform distribution.

Key words: vacuum electron beam welding; welding processing parameters; Ti₂AlNb/TC18 alloy; welding interface; elevated temperature tensile properties; microstructure