Effects of alloying elements on the stability and mechanical properties of β-Ti_0.5X_0.5 (X = V, Cr, Mn, Fe; Nb, Mo, Tc, Ru; Ta, W, Re, Os) alloys according to first-principles calculations

The stability and mechanical properties of β-Ti_0.5X_0.5 alloys have been systematically investigated by means of first-principles calculations based on density functional theory. The present work has demonstrated that the considered Ti_0.5X_0.5 alloys are stabilized as β phase and that the formation energy decreases with respect to the introduced transition metal elements X. The results show that the mechanical parameters, including the Young's modulus E, shear modulus G and bulk modulus B, increase with the increase of valence electron concentration of X in the same period. The Poisson's ratio ν and B/G ratio indicate that β-Ti_0.5X_0.5 alloys are essentially ductile materials. According to the stretching model, the tensile strength of the Ti_0.5X_0.5 alloys significantly increases simultaneously. An analysis of the charge density and electron localization function (ELF) shows that the observed enhancement in tensile strength is mainly derived from the improvement in bond strength between Ti and X induced by the different valence electron concentrations. The present research may provide beneficial guidance for improving the strength-toughness compatibility of Ti-based alloys.