Scanning Electron Microscopy and Roughness Measurements of the Wear Scars Generated in Carbide Composites by the ASTM B611 Test

摘要

Abrasion resistance of conventional cemented carbides such as WC-Co where the hard particles are typically a few microns in size and non-conventional carbide composites such as DC carbide composites where the hard phase is a sintered WC-Co pellet several tens of microns in size was measured using the ASTM B611 wear test. All the wear data are uniformly expressed in terms of wear coefficients, defined as volume lost per unit load and unit sliding distance. Wear coefficients of cemented WC-Co show excellent correlation to bulk hardness. Wear coefficients for DC carbide, however, deviate significantly from this trend and the values are exceptionally low for their level of hardness. Typical wear scars generated by the B611 test are asymmetric with the exit side more sharply defined than the entry side. Roughness measurements along the length of the wear scar show that the roughness varies in a systematic way from the entry to the exit side. For WC-Co cemented carbides the average and maximum roughness values at the exit end and the peak of the roughness profile show good correlation to bulk hardness. Roughness values for the DC carbides also fall on the same lines. Scanning electron microscopy and energy dispersive analysis of the wear scars show embedded and fractured alumina particles of different sizes and amounts in all of the wear scars. For DC carbides the embedded alumina particles are found preferentially in the binder areas, whereas for WC-Co cemented carbides, the alumina particles are more uniformly distributed. We suggest a mechanism for the preferential embedding of alumina particles in the binder areas of DC composites and claim that such preferential embedding is responsible for the observed low wear coefficients for these composites as compared to conventional WC-Co.