Effect of stoichiometry on the structural properties and the electronic structure of intermetallics: anti-phase boundary energies in FeAl and NiAl

As a possible means of alleviating the severe brittleness in the B2 compounds FeAl and NiAl, the all-electron self-consistent total energy linear muffin-tin orbital (LMTO) method was employed to investigate the possibility of lowering the 〈111〉 anti-phase boundary (APB) energies by changing compositions in FeAl and NiAl. For APB's created in the regions with excess Fe (or Ni) atoms, APB energies for the model systems, Fe_0.6Al_0.4 and Ni_0.6Al_0.4, were found to be one order of magnitude smaller than those for stoichiometric B2 FeAl and NiAl, respectively. Apparently, the activation of 〈111〉 slip became possible in these cases. On the other hand, the APB energies remained at about the same as those in stoichiometric FeAl and NiAl for APB's occurring in regions with equal numbers of Fe (Ni) and Al atoms, implying that the activation of 〈111〉 slip in these regions was not eased.