The structural, mechanical and electronic properties of Ti-Al-based compounds by first-principles calculations

The first-principles calculations with density functional theory were performed to investigate the effects of transition metal elements (Mo, Cu, Fe, Ni and Nb) on the physical properties of the Ti-Al-based compounds. Our optimized crystal parameters are in good agreement with the previous theoretical and experimental values. The mechanical stability is verified by the independent elastic constants. The B/G and Poisson's ratio ν both show that Al₆TiMo is brittle, while other compounds exhibit ductility. The values of compression anisotropy of the compounds are small, but the shear anisotropy of AlCu₂Ti and AlNi₂Ti is much more intense than that of other compounds. The anisotropy in elastic properties of AlFe₂Ti and AlNbTi₂ is smaller than that of the others. It can be seen that the capacity to compress along c-axis is smaller than that along a-axis and b-axis for AlNbTi₂. For AlNbTi₂, the anisotropy of the bulk modulus along a-axis relative to b-axis is more insignificant than that along c-axis relative to b-axis. The hardness and Debye temperature verify that AlFe₂Ti has the greatest resistance to the plastic deformation and more intense inter-atomic bonding force, respectively. Band structures and DOS are used to investigate the electronic properties. The band structures without band gaps show that these ternary Ti-Al-based compounds are conductors. DOS shows the interactions between elements and gives the bond properties. Density of states and charge density both show the strong covalent properties of AlFe₂Ti by the hybridization between Fe-3d and Ti-3d states.