A study of the tribological behaviour of three carbon-based coatings, tested in air, water and oil environments at high loads

Diamond-like carbon (DLC) coatings exhibit excellent tribological properties in dry sliding conditions. Two recently developed carbon-based coatings (Graphit-iC and Dymon-iC) have been shown to exhibit very high sliding wear resistance (specific wear rates of 1×10−17 m3 N−1 m−1) and low friction under high applied loads when tested in air. In this paper, the sliding wear behaviour of these coatings (along with a commercially available DLC) is examined in three test environments, namely, air, water and oil. The commercially available DLC failed under contact pressures of >1 GPa, irrespective of environment, whereas both the Dymon-iC and Graphit-iC coatings were able to run under pressures of >2 GPa. The Graphit-iC coating exhibited low wear rates under all three environmental conditions. However, both of the a-C:H coatings (Dymon-iC and commercially available DLC) failed rapidly when tested in water. In air and oil environments, the Dymon-iC coating exhibited lower wear rates than the Graphit-iC coating. Reasons for this behaviour are proposed.