Shielding model of fracture in WC-Co

A shielding model of fracture in WC-Co alloys, aiming to explain an unexpectedly frequent occurrence of the binder phase on the crack surface, is presented. The shielding of the crack tip is caused by the multiligament zone formed by ductile binder ligaments behind the crack tip. The shielding leads to a decrease of the crack tip opening displacement and the plastic zone size ahead of a blunting crack tip. Consequently, normal stresses build up and, as a result, the cleavage of matrix is facilitated even under a lower local intensity factor perceived by crack tip. The co-operation of the cleavage of the matrix and the tearing of binder ligaments results in a meandering path of crack with a surprisingly high ligament area fraction. The partition between carbide and binder phase related fracture is predicted. The composite toughness is linked to the mechanical and microstructural parameters of WC-Co composite by a simple relationship.