On the core structure and mobility of the <100>{010} and <100>{011-bar } dislocations in B2 structure YAg and YCu

Dislocations are thought to be the principal mechanism of high ductility of the novel B2 structure intermetallic compounds YAg and YCu. In this paper, the edge dislocation core structures of two primary slip systems <100>{010} and <100>{011-bar 1} for YAg and YCu are presented theoretically within the lattice theory of dislocation. The governing dislocation equation is a nonlinear integro-differential equation and the variational method is applied to solve the equation. Peierls stresses for <100>{010} and <100>{011-bar 1} slip systems are calculated taking into consideration the contribution of the elastic strain energy. The core width and Peierls stress of a typical transition-metal aluminide NiAl is also reported for the purpose of verification and comparison. The Peierls stress of NiAl obtained here is in agreement with numerical results, which verifies the correctness of the results obtained for YAg and YCu. Peierls stresses of the <100>{011-bar 1} slip system are smaller than those of <100>{010} for the same intermetallic compounds originating from the smaller unstable stacking fault energy. The obvious high unstable stacking fault energy of NiAl results in a larger Peierls stress than those of YAg and YCu although they have the same B2 structure. The results show that the core structure and Peierls stress depend monotonically on the unstable stacking fault energy. (condensed matter: structure, thermal and mechanical properties)