Tribological behaviour of WC/C coatings operating under different lubrication regimes

The aim of the present work was to investigate the tribological behaviour of oil-lubricated WC/C coated surfaces, operating under different lubrication regimes. Tests were performed in a pin-on-disc and a load-scanning test rig, where WC/C coated samples were loaded against coated and uncoated ones, while the steel–steel combination was used as a reference. All material combinations were tested under starved, boundary and elastohydrodynamic (EHD) lubrication conditions, using four lubricants; a pure poly-alpha-olefin (PAO) oil, PAO mixed with commercial sulfur-based extreme-pressure additive or zincdithiophosphate-based anti-wear additive and a fully formulated gearbox oil. The results of this investigation show that application of WC/C coating, especially when using a WC/C–steel combination, gives faster and smoother running-in behaviour and improved tribological properties of the contact surfaces running under starved or boundary lubrication conditions. However, the combination of two coated contact surfaces leads to increased wear and high friction under EHD lubrication conditions.