Microstructure/property relationships in the slurry erosion of tungsten carbide–cobalt

The slurry erosion performance of ultrafine WC–Co composites sintered from powder produced through the spray conversion process has been evaluated and compared to that of conventional materials. Slurry erosion testing has been carried out using the jet impingement method and slurry composed of water and 500 μm diameter silica sand. The erosion resistance of WC–Co hard metals is seen to increase dramatically as the grain size decreases below about 1 μm, with the result that ultrafine WC–Co may be up to three times more erosion resistant than the closest conventional material. This increase in erosion resistance is considerably higher than the corresponding increase in hardness, which is at most 25%. Furthermore, these increases are not achieved at the expense of fracture toughness, which is maintained at a similar level to that of conventional materials. The results of microscopic examination indicate that this rapid increase in erosion resistance may be due to a transition from a predominantly brittle to a predominantly ductile mode of erosion. The transition results from a change in the relative dimensions of the microstructure and the erodent impact zone. This hypothesis is supported by the results of a qualitative investigation into the dependence of erosion rates on impact angle. These show that as the grain size of the material decreases, erosion occurs preferentially at lower impact angles.