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.