DEFORMATION-BEHAVIOR OF B2 TYPE ALUMINIDES - FEAL AND NIAL

First-principles calculations of the elastic constants, shear fault energies, cleavage strength, and bonding charge density of NiAl and FeAl are presented. For NiAl, we find that the dissociation of <111> superdislocations into partial dislocations is unlikely, because of a high antiphase boundary (APB) energy and a weak repulsive elastic force between partial dislocations. The APB energy of FeAl is found to be highly anisotropic with respect to different slip planes. FeAl has a high ideal cleavage strength as a result of the directional d-bond formation at the Fe sites. The strong ordering behavior of NiAl is explained in terms of the repulsive interaction between Al atoms as a result of the Al-to-Ni charge transfer and the atomic size difference of Ni and Al. The active slip plane of {112BAR} in FeAl at low temperatures is predicted on the basis of the anisotropic elastic coupling effect of non-glide stresses. The spontaneous glide decomposition of the <111> superdislocation in NiAl, which can be a source for <100> slip, is also discussed.