Plastic incompatibility and crack nucleation during deformation on four independent slip systems in tungsten carbide-cobalt

Abstract

The problem of slip transfer across grain boundaries is considered for the case of a hexagonal material that is plastically inextensible along [0001]. The discontinuity in tensile strain that must necessarily exist across a grain boundary is a cause of intergranular and transgranular cracking on the basal plane. Intergranular cracking at many grain junctions and two-grain junctions is shown to arise out of in-plane and normal strain differences across grain boundaries, respectively. Experimental evidence from deformed WC-Co is adduced to support these predictions. Transgranular cracking on the basal plane is found to occur only in coarse grained material. Thin (≈ 500 Å) layers of cobalt between carbide grains do not appear to appreciably affect the onset of cracking if it is expected from an incompatibility standpoint. The implications of these results are discussed for the general case of deformation of brittle solids, both with and without a superimposed constraining pressure.