Investigation on the microstructure and mechanical properties of high-Nb TiAl/Ti600 alloy electron beam welded joints

The electron-beam welding of high-Nb TiAl/Ti600 alloy was investigated in this paper to provide theoretical and experimental basis for the high-quality welding of high-Nb TiAl/Ti600. In this paper, optical microscopy, scanning electron microscopy and X-ray diffraction equipment are used to analyze the welding samples. The results showed that the joint was susceptible to solid-state cracking. Owing to fast cooling rate of electron beam welding, the acicular α₂-Ti₃Al phase and a little α-Ti phase were formed in the FZ (fusion zone), while the HAZ (heat affected zone) of high-Nb TiAl was composed of laths and equiaxial microstructure, and the acicular α'phase precipitated from the HAZ of Ti600 alloy. The joint exhibited a peak value in micro-hardness that occurred at the far end of FZ near the fusion line of high-Nb TiAl alloy and the hardness decreased from the weld seam to the both sides of base metals. The ultimate tensile stress of the as-welded specimen was 516 MPa, and the fracture occurred at the FZ on the side of TiAl alloy. It exhibited brittle cleavage fracture mode and also presented a characteristic of transgranular fracture.