Microstructure/property relationships in the cavitation erosion of tungsten carbide-cobalt

The cavitation erosion performance of a range of tungsten carbide-cobalt (WC-Co) composites of varying grain sizes and cobalt contents has been evaluated using a stationary-specimen vibratory cavitation erosion rig. The WC grain size of the materials varied between 0.5 and 3 mu m and the cobalt content between 6 and 15 wt.%. Two distinct regimes are observed in the cavitation erosion of the WC-Co grades tested: for materials with a WC grain size below 1 mu m, the erosion resistance increases with decreasing cobalt content, while for materials with a WC grain size above this lever, this trend is reversed. Microscopic examination of the eroded surface shows this transition to coincide with a change in material removal mechanism: sub-micron materials experience bulk material loss, while coarser materials display a localised response to erosive attack, which results in the preferential removal of the cobalt phase and the consequent loss of unsupported WC grains. It is proposed that this transition is related to a scaling effect similar to that observed in the particle erosion of composite materials. The relationship between the erosion response of the composite and its microstructural and mechanical properties in each regime is evaluated and discussed. (C) 1999 Elsevier Science S.A. All rights reserved.