Simulation of Co Binder Failure in WC-Co Hardmetals

Abstract

WC-Co hardmetals are composite materials of brittle phases, including WC, and a ductile phase Co. The Co is present in typical volume fractions of 10%. Fracture is characterised by cleavage failure of the brittle phases and ductile failure of the Co. In this paper attention is focused on the highly constrained Co binder layers that fail by void growth and coalescence. Cracks traverse the layers or propagate close to the Co/brittle phase interfaces. The growth of a periodic arrangement of voids is simulated. The modelling involves a detailed description of the microstructure incorporating a physically based, finite deformation, rate dependent, crystal theory of plastic slip. The theory is implemented using the finite element method. The effects of void shape, overall stress state and binder layer thickness on void growth behaviour are assessed. The simulated void growth behaviour is used to analyse failure close to the interface. For void growth, comparisons are made to the predictions of phenomenological constitutive theories. The effect of re-meshing to improve the accuracy of the simulations is assessed.