Investigation on electronic structures and mechanical properties of Nb–doped TiAl2 intermetallic compound

The electronic structures and mechanical properties of Nb–doped TiAl₂ intermetallic compounds have been investigated using the first–principles method based on the density functional theoretical framework. The calculated results indicate that the structural symmetry of orthorhombic TiAl₂ has been changed after the Al or Ti atoms are replaced by the Nb atoms. The formation energy of the systems in which Al atom replaced by Nb is lower than that of Ti atom replaced by Nb. Accordingly, the Nb atoms are more likely to occupy the sites of Al atoms to form a stable structure when the Nb atoms are introduced into orthorhombic TiAl₂ compound. Additionally, the formation energy of the doped systems increases with the increase of Nb atom percentage. Nb doping weakens the covalent bonding between Ti and Al atoms and enhances the metal bonding between them. The band structures of Nb–doped TiAl₂ systems also indicate that they all have metallic conductivities, which is beneficial to decrease the brittleness of orthorhombic TiAl₂ intermetallic compounds at room temperature. Compared with those systems in which Ti atoms replaced by Nb atoms, the ductility of the Nb–doped TiAl₂ system in which Al atoms are replaced by Nb atoms has been improved better. It is attributed to the density of state near Fermi energy level being increased after Al atoms being replaced by Nb atoms. The fracture strength of Nb–doped TiAl₂ systems is both better than that of the purely TiAl₂, especially in the system of Ti atoms replaced by Nb atoms.