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

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 132 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. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.