The effect of electronic structure on the defect properties of FeAl

First-principles local-density-functional calculations have been used to investigate the defect properties of FeAl: (1) the ordering behavior and equilibrium point defects; (2) the binding interactions among vacancies; and (3) the mechanism underlying the hydrogen-induced embrittlement effect. The point defect structure is dominated by substitutional antisite defects on both sublattices and thermal vacancies on the Fe sublattice. It is predicted that the binding between vacancies is strongly attractive when vacancies are aligned along the [100] direction, and becomes weakly repulsive when vacancies are [110]a or [111]a apart (where a is the lattice constant). The binding interaction between vacancies is found to manifest the oscillations in the vacancy-induced charge density on neighboring lattice sites. Energetically, vacancies (and/or vacancy clusters) provide favorable lattice sites for hydrogen segregation. The hydrogen-induced embrittlement is explained in terms of a charge transfer mechanism and the localization behavior of induced charge at the hydrogen site.