Effect of heat distribution on microstructure and mechanical properties of electron beam welded dissimilar TiAl/TC4 joint

Microstructure and mechanical properties of electron beam welded TiAl/TC4 joints are sensitive to heat input due to the complex solid-state transformation of the weld. Experiments and numerical simulations were conducted to investigate the effect of heat distribution on microstructure and mechanical properties of the joint in detail. The brittle α2-Ti3Al dominated microstructure was generated in the weld that underwent high peak temperature and rapid cooling rate during welding process. Thermodynamic analysis revealed that the Gibbs free energy of formation of Ti3Al was greatly lower than that of TiAl at a high temperature (≥ α single phase region), which is benefit for the formation of α2 phase. Brittle α2 phase was also generated in the heat affected zone on TiAl side, with decreased content from the weld to base metal owing to the gradually reduced heat flux. The ambient temperature tensile strength of the joint was 386.3MPa. All joints were fractured along the fusion line and exhibit brittle fracture characteristics.