A first-principles study of site occupancy and interfacial energetics of an H-doped TiAl-Ti ₃Al alloy

We investigate the site occupancy and the interfacial energetics of TiAl-Ti ₃Al binary-phase system with H using a first-principles method. H energetically prefers to occupy the Ti-rich octahedral interstitial site because H prefers to bond with Ti rather than with Al. The occupancy tendency of H in the binary phase TiAl-Ti3Al alloy from high to low is α ₂-Ti ₃Al to γ/ α ₂ interface and γ-TiAl, because the decrease of the Ti local concentration is in the same order. We demonstrate that H can largely affect the mechanical properties of the TiAl-Ti ₃Al system. On the one hand, H at the interface reduces the interface energy with the H ₂ molecule as a reference, implying the TiAl/Ti ₃Al interface is stabilized. On the other hand, the ratio between the cleavage energy and the unstable stacking fault energy decreases after H-doping, indicating H will reduce the ductility of the TiAl/Ti ₃Al interface. Consequently, the mechanical property variation of TiAl alloy due to the presence of H not only depends on the amount of TiAl/Ti3Al interfaces but also is related to the H concentration in the alloy.