Fracture of WC-Co alloys: an example of spatially constrained crack tip opening displacement

Abstract

This paper attempts, both experimentally and theoretically, to account quantitatively for the propagation of cracks in WC-Co alloys. Evidence is presented which shows that cracks propagate through the ductile Co phase. It is further shown that the square of the quasi static stress intensity factor ($K$$_{\text{IC}}$) of a slowly propagating crack is linearly related to the Co mean free path. On the assumption that crack tip plasticity cannot extend beyond a single interlayer of Co it is found that the yield stress must be close to twice the theoretical shear stress of Co. Thus, for a particulate composition which consists of grains sufficiently resistant to cleavage and plastic yield, and is bonded by a matrix which is ductile and not susceptible to cleavage, ($K$$_{\text{IC}}$) can be calculated. It therefore appears possible, for the first time, to predict accurately from first principles, the fracture toughness of a real elastic-plastic body.