Structure-property relationships in liquid jet erosion of tungsten carbide hardmetals

The National Physical Laboratory has recently commissioned a liquid jet erosion rig capable of infinitely variable impingement velocities and slurry erodent volume fractions. Initial work using the new tribometer is being focussed on hardmetals based on tungsten carbide, either with a cobalt binder or cobalt/nickel binder. Investigations have been conducted into correlating wear behaviour with conventional parameters used for characterising hardmetals (hardness, binder linear intercept and WC grain size) and also the relative contributions of ductile and brittle response to the impinging slurry. Electron microscopy has been used to relate quantitative material loss due to erosion with prevailing wear mode(s) and to clarify structure-property relationships. The WC based hardmetals show an inverse log-linear relationship between hardness and volume loss, but with microstructural determinants also factoring in. Brittle fracture of WC grains and pluckout (undermining) is seen on wear surfaces. Erosive material loss correlated with WC grain linear intercept for a fixed binder content. In general, using an impingement angle of 45° (as opposed to a normal incidence stream) induced less volume loss and often a milder wear regime could be seen to be operative under these conditions.