Generalized stacking-fault energies for TiA1: mechanical instability of the (111) antiphase boundary

Generalized stacking-fault energies for the (111) and (100) planes of stoichiometric TiAl are calculated within the framework of density functional theory in the local-density approximation and the full-potential linearized-augmented-plane-wave method. The most striking result is the mechanical instability of the (111) antiphase boundary (APB) with respect to shear along [112] towards the complex stacking fault (CSF). Consequently, the energy of the (111) APB is larger than the energy of the CSF which in turn is about twice the energy of the superintrinsic stacking fault. Implications for the dissociation of superdislocations in stoichiometric TiAl are discussed.