Effects of boron on the mechanical properties of the TiAl-Ti₃Al alloy: A first-principles investigation

Employing a first-principles method in combination with the empirical criterions, we have investigated the site preference of boron (B) and its effect on the mechanical properties of the binary-phase TiAl-Ti₃Al alloy. It is found that B energetically prefers to occupy the Ti-rich octahedral interstitial site, because B is more favorable to bond with Ti in comparison with Al. The occupancy tendency of B in the TiAl-Ti₃Al alloy is the TiAl/Ti₃Al interface > Ti₃Al > TiAl, thus B tends to segregate into the binary-phase interface in the TiAl-Ti₃Al alloy. The charge density difference shows that B at the TiAl-Ti₃Al interface will form strong B-Ti bonds and weak B-Al bonds, leading to the significant increasing of the cleavage energy (γcl) and the unstable stacking fault energy (γus). This indicates that the presence of B will strengthen the TiAl/Ti₃Al interface, but block its mobility. Further, the ratio of γcl/γus of the B-doped system is 4.63%, 8.19% lower than that of the clean system. Based on the empirical criterions, B will have a negative effect on the ductility of the TiAl-Ti₃Al alloy.