Microstructure Evolution and Its Effect on Mechanical Properties in an Electron Beam Welded β-Solidified TiAl Alloy

TiAl alloys are susceptible to cracks during electron beam welding because their limited ductility cannot accommodate the stress generated under fast cooling rate. In this work, pre-heating and post-heating via defocused electron beam were used to obtain well-welded joints without cracks. Lower crack sensitivity of joints was attributed to the microstructure evolution to obtain more ability of stress accommodation with the increasing heating beam current and heating time. Long-time pre-heating of 5 min and post-heating of 12 min led to reduced volume fraction of residual β ₀ phase with the growth of α ₂/γ lamellar colonies in the fusion zone (FZ). The refined microstructure of FZ contributed to the highest hardness of the FZ, and the fracture happened at the base material (BM) in tensile tests, indicating that the tensile properties of the welding seam surpassed that of the BM. This work provides an effective way to obtain TiAl joints with better mechanical properties of the welding seam than that of the BM, which is a breakthrough in the welding of TiAl alloys.