Effect of co-alloying elements on the structural stability, elastic, ductility and thermodynamic properties of TiAl intermetallic compound

Abstract

The considerable lack of room temperature ductility and toughness is widely recognized as an important limitation for the commercialization of titanium aluminides in industrial engineering. To meet this target, we optimize a new polycrystalline alloy based on Gamma-titanium aluminide co-alloying with Mo–Cr, Mo–Nb and Mo–Re atom pairs that simultaneously satisfy the physical criteria of workability using the density functional theory within the framework of the generalized gradient approximation. The formation enthalpy calculations showed that the Ti–Ti sites remain the preferential sites of Mo–Cr and Mo–Nb atomic defects, while the Mo–Re elements tend to occupy Ti–Al sites. The elastic properties systematically suggest that TiAl–Mo–Nb system is further resistant to tensile deformation along c-axis and a-axis (b-axis). In addition, the co-alloying Mo–Re atom pair exhibit improved mechanical performance compared to the other systems. These trends are confirmed by analyzing the electronic structure. Using quasi-harmonic approximation, thermodynamic properties were also predicted by including the description of the temperature. The results of co-alloying with molybdenum and rhenium atoms confirm effectively their usability in turbine blades and engine-valves made of Gamma-TiAl alloys.