Cleavage fracture and crack tip dislocation emission in B2 NiAl: An atomistic study

Abstract

The crack tip response to various loading conditions in NiAl is studied atomistically. The immediate surroundings of the crack tip are described atomistically using an embedded atom potential. An elastic finite element region provides the atomistically modelled crack tip with realistic boundary conditions. In agreement with experimental observations, perfectly brittle cleavage is observed only for the {110} crack plane. In contrast, mode I cracks on the {100} plane either follow a zig–zag path, or emit dislocations. Cracks injected on high index planes emit dislocations, deviate from the original crack plane onto a {110} cleavage plane or lead to (non-crystallographic) rupture. Dislocation emission was studied further under mixed mode loading. Irrespective of dislocation character, dislocation emission is correlated with an almost constant mode II energy release rate on the glide plane. The importance of these observations for the understanding of brittle fracture and dislocation nucleation are discussed in detail.