Sliding wear behaviour of HVOF sprayed WC–Co coatings deposited with both gas-fuelled and liquid-fuelled systems

WC–Co thermally sprayed coatings are now widely used in a range of industries to combat wear. During spraying of WC–Co coatings, there is a decomposition involving dissolution of the hard phase into the molten binder; as such, the coatings are often made up of WC along with other carbides in a matrix consisting of tungsten and carbon dissolved in the cobalt. High velocity oxy-fuel (HVOF) spraying is seen as the pre-eminent process for deposition of such coatings. There have been moves in the industry to spray coatings with liquid-fuelled systems rather than gas-fuelled guns, since the former lead to shorter residence times of the particles in the flame and lower temperatures, both of which lead to less dissolution of WC and decomposition of the coating. This paper presents work concerning the sliding wear behaviour of WC–Co coatings HVOF sprayed with both liquid-fuelled (HVOLF) and gas-fuelled (HVOGF) systems and demonstrates that with a dense powder feedstock, the HVOGF deposited coating is superior to the HVOLF deposited coating. The poorer performance of the HVOLF-sprayed coating is associated with mechanical damage to the WC–Co powder particles as they impact with the substrate resulting in carbide cracking and a reduction in the integrity of the bond between the carbide particles and the matrix phase.