First-principles determination of the tensile and slip energy barriers for B2 NiAl and FeAl

The Griffith energies and the unstable stacking fault energies for FeAl and NiAl are investigated using the highly precise full potential linearized augmented plane wave method. Large multilayer relaxation is obtained through atomic force and total-energy calculations. The unstable stacking fault energies for <100> and <110> slips in NiAl(001) are 1.3 and 2.2 J/m², respectively. They are much smaller than the tensile cleavage energy, 5.4 J/m², and indicate that the major deformation mode in stoichiometric NiAl is <100> slip, a result which agrees with experiment. For FeAl(001), the unstable stacking fault energies are much higher and are equally anisotropic (2.4 and 3.9 J/m² for <100> and <110> slips, respectively). We found that p-d hybridization plays an important role at E_F for NiAl but not for FeAl, which may contribute to these different mechanical properties.