Friction and Wear of Diamond-Like Carbon Coatings Lubricated With Biodegradable Oils

The tribological behaviour of coated machine components lubricated with a biodegradable saturated ester and unsaturated ester oil has been studied. Different diamond-like carbon-based coatings (DLC) were selected as low friction coatings: pure DLC, Si-doped, Ti-doped and W-doped DLC. The performance of the studied ester oils has been compared with sunflower oil and mineral oil lubrication as reference. The oils were all additivated in the same way with conventional anti-wear (AW) and extreme pressure (EP) additives. Different tests have been performed: disc on disc, ball on disc and block on ring tests give an overview of the influence of different sliding modes. The effect of the lubricant on a coated system compared to the use of the coated system without lubrication is clear for the wear, but less obvious for the friction. It was found that DLC/DLC contacts lubricated with biodegradable lubricants show similar friction as steel/steel contacts. The effect of the different types of base oil is independent of the coating type. Additive activity which was clear in steel/steel contacts was not obvious in DLC/DLC contacts.