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