BONDING MECHANISMS AND POINT-DEFECTS IN TIAL

The bonding mechanism and point defect structure in TiAl were investigated using a first-principles quantum mechanical calculation. The most remarkable feature found in the calculated binding charge density is the polarization of the p-electron at the aluminum sites, which gives rise to a large bond bending force between the Ti and Al layers. For the point defects, the absence of structural vacancies is predicted in TiAl, and the deviations from stoichiometry are accommodated by the substitutional antisite defects on both sublattices. High vacancy formation energies are obtained, which are closely related to the strong Ti-Al bonding and the similar atomic radii of Ti and Al.