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 FeA l and NiAl are investigated using the highly precise full potential li nearized augmented plane wave method. Large multilayer relaxation is o btained through atomic force and total-energy calculations. The unstab le stacking fault energies for [100] and [110] slips in NiAl(001) are 1.3 and 2.2 J/m(2), respectively. They are much smaller than the tensi le cleavage energy, 5.4 J/m(2) 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 m uch higher and are equally anisotropic (2.4 and 3.9 J/m(2) for [100] a nd [110] slips, respectively). We found that p-d hybridization plays a n important role at E(F) for NiAl but not for FeAl, which may contribu te to these different mechanical properties.