Ab initio calculation of bulk and defect properties of ductile rare-earth intermetallic compounds

Abstract We have used ab initio calculations to examine various properties of YAg and YCu, two members of a class of fully ordered stoichiometric intermetallics with the CsCl-type B2 lattice. These two alloys, and numerous similar compounds, have been found to have significant polycrystalline ductility, in some cases exceeding 20% ductility in tension. Calculated bulk properties are consistent with experimental data, where available, including lattice parameters, elastic constants, and stability with respect to the B27 FeB structure. Anti-phase boundary energies are large, consistent with the high degree of orders in these systems, and with the absence of b = 〈 1 1 1 〉 slip in single crystal experiments. However, unstable stacking faults associated with b = 〈 1 0 0 〉 slip are quite low, in contrast with NiAl where these energies exceed those of the anti-phase boundaries.