Intergranular cracking in WC-6% Co: an application of the von mises criterion

Abstract

Intergranular cracks between WC grains in the plastic zones of indentations in WC-6% Co have been analyzed using transmission electron microscopy. The primary slip systems in the carbide are of the type {11̅00} <112̅3>. Such a combination can generate only four independent strains, one less than the five required for compatible plastic flow in a polycrystalline aggregate. In particular, WC is incompressible along [0001]. A model is proposed to predict the likelihood of the failure of a grain boundary, given both its crystallographic orientation and those of the two adjoining grains. The experimental evidence on both cracked and uncracked grain boundaries bears out the theoretical predictions, i.e. that cracking is a consequence of large normal stresses acting on a boundary and arising from the incompatible deformation of neighboring grains.