Narrow Results

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 $({\gamma }_{\mathrm{\text{cl}}})$ and the unstable stacking fault energy $({\gamma }_{\mathrm{\text{us}}})$. This indicates that the presence of B will strengthen the TiAl/Ti₃Al interface, but block its mobility. Further, the ratio of ${\gamma }_{\mathrm{\text{cl}}}$/${\gamma }_{\mathrm{\text{us}}}$ 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.