Sliding wear behavior of WC–12% Co coatings at elevated temperatures

Abstract

WC–Co coatings with low degree of decomposition were thermally sprayed by a high velocity oxy-fuel system from three agglomerated WC–12 mass% Co powders with different carbide grain size distributions. Dry sliding friction and wear behavior of the WC–12% Co coatings was investigated by using sintered alumina (Al2O3) as the mating material at 200 °C, 300 °C and 400 °C. The friction coefficient of these WC–Co/alumina pairs was nearly constant regardless of the test temperature and the carbide grain size of the coatings. The specific wear rate of the coatings increased with increasing the carbide grain size at a given testing temperature. It decreased with increasing the temperature for a given carbide grain size. The specific wear rate was reduced by more than one order of magnitude when the test temperature was increased from room temperature to 400 °C. The microscopic analyses of the worn tracks showed that the tribofilm formed at higher temperature is denser and more adhesive to the underlying surface, thus providing more surface protection against wear. The results show that the formation of dense and adhered tribofilms plays an important role on the low sliding wear rate of the coatings at elevated temperatures.