Tribological performance of a DLC coating in combination with water-based lubricants

The tribological behaviour in water-based environments has been studied for a tungsten carbide-doped DLC coating (WC/C) deposited by physical vapour deposition (PVD) on bearing steel. Several tribological test equipments have been used to characterise the wear rate, coefficient of friction and resistance to seizure of the coated system, in comparison with uncoated bearing steel surfaces. It was observed that the wear was decreased and the coefficient of friction reduced in pin-on-disc measurements for poor lubricants. Further, the resistance to seizure in the four-ball method was improved by a factor of approximately three. Results from Reichert measurements showed a decreased wear rate and also a very pronounced running-in behaviour of the coating for some water-based lubricants. It has been shown that the performance of tribological systems with water-based lubricants can be significantly improved with this type of DLC coating.