The Impact of the Lubricant Additive Package on the Tribological Performance of Diamond-Like Carbon Coatings in Simulated Cam-Follower Conditions

摘要

Diamond-like carbon (DLC) coatings are recognised as a promising way to reduce friction and increase wear performance of automotive parts and are currently being introduced for some engine and transmission components. DLC coatings provide new possibilities in the improvement of the tribological performance of automotive components beyond what can be achieved with lubricant design alone. The lubricant design has a significant impact on coating durability and performance. Lubricants are currently designed for metallic surfaces, the tribology of which is well defined and documented. DLC does not share this depth of tribological knowledge, thus its practical implementation is stymied. In this work, a DLC coating is tested in a lubricated contact simulating a cam/ follower interface within an automotive engine. The role of lubricant/surface interactions is investigated experimentally against a cast iron counter-body. The tribofilm formation process is characterized chemically and mechanically using EDX mapping and nano-indentation. The development of friction is related to the dynamics of tribofilm formation and tribofilm time dependence is investigated. The emphasis of this paper is on how the coating structure and composition can be adapted for optimal interaction with a fully formulated lubricant to enhance the overall tribological system performance.