Impede Crack Propagation Research Articles

On the Deformation of WC–Co Cemented Carbides

The deformation characteristics of WC–Co cemented carbide composites, with emphasis on the binder phase, were investigated. The binder, which is present mainly in the fcc modification in the as-sintered condition, was found to deform through the formation of hcp lamellae. This initially gives the binder the ability to deform in full compatibility with the carbide skeleton. Ultimately the partially transformed binder is unable to fulfil the compatibility requirements and loses its ability to impede crack propagation. Simultaneously the carbide skeleton, which deforms plastically by a glide mechanismin each WC grain, starts to break up and fracture of the composite occurs.

The interaction of cleavage cracks with inhomogeneities in sodium chloride crystals

Abstract Single crystals of sodium chloride have been treated by electrodiffusion so that they contain small voids and particles of gold. Cleavage cracks of known velocities have been introduced into these crystals, and the effect of the inhomogeneities on crack propagation has been studied. Measurements of the velocity of cracks have indicated that the inhomogeneities impede crack propagation. Subsequent examination of the cleavage surfaces by optical microscopy and, in greater detail, by electron microscopy of surface replicas, has revealed characteristic patterns of steps at the inhomogeneities. These have been explained in terms of cleavage steps and slip steps which result from dislocations that are generated at the front of a crack when it undergoes changes of velocity and shape at the inhomogeneities. These observations may be applied to the problem of ‘crack-stopping’ in certain ceramic materials.