Wear behaviour of WC–Co HVOF coatings at different temperatures in air and argon

The wear behaviour of tungsten carbide–cobalt (WC–Co) high-velocity oxy-fuel coatings within the range of room temperature (RT) to 800°C in air and RT to 650°C in argon was studied using a ball-on-disc tribometer. The worn track morphologies, compositions and oxide phases after the tests were analysed by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction analysis and Raman spectroscopy. The correlation between the oxidation and wear of WC–Co coatings was investigated. Results show that oxides, as well as the oxidation of coatings, have an important role during the tribological process of WC–Co coatings. The volume loss of WC–Co coatings in air is low at RT to 600°C, which indicates that oxidation inhibits wear. Friction promotes the formation of CoWO4. CoWO4 can reduce friction and wear, and enables the coating to maintain good tribological properties even at 600°C. Above 600°C, the coating oxidises vigorously and its property deteriorates rapidly, which cause serious wear. In argon, the volume loss of WC–Co coating is significantly higher than that in air at RT to 600°C. Wear decreases as temperature rises because of the gradual formation of oxides. Consequently, WC–Co coatings should not be used as wear-resistant coatings in O-deficient environments at RT or at elevated temperatures.