A novel zipper shape joint for improving microstructure and mechanical property of electron beam welded TiAl joint

TiAl alloy is sensitive to welding cracks and exhibits brittle nature at room temperatures. The formation of the α2-Ti3Al phase coupled with high welding residual stress has been proved to be the key factor triggering the cracking of the joint. To improve the microstructure of the weld, a zipper shape joint is designed to decrease the cooling rate of the joint. Finite element simulation analysis of the traditional line-shape joint and the zipper shape joint was carried out. The results reveal that the special zipper shape design effectively decreases the cooling rate of the joint than the straight-line shape joint. The zipper shape can play a role in preheating and post-heat treatment during the welding process. Compared with the straight-line shape joint, the high temperature (above 750 °C) dwelling time of the zipper shape joint is greatly prolonged, which promoted the α → γ phase transformation. However, such weld path also causes stress concentration in the corner region of zipper shape weld bead. Though welding cracks still exist, the crack frequency of the zipper shape joint is decreased obviously. The tensile tests also exhibit that the strength of the zipper shape joint reaches 417 MPa, 40.4 % higher than that of the straight-line shape joint of 297 MPa. Hence, joint shape design can be regarded as a promising direction for further investigations referring to crack control of TiAl joints.