Hydrogenated Diamond-Like Carbon (H-DLC) Thin Film Development for Space Mechanisms with Enhanced Tribological Performance

Diamond-like carbon (DLC) self-lubricating coatings have recently been explored as promising tribological solution for transmission components in rolling systems such as gears and bearings. These coatings demonstrate excellent performance under both atmospheric and vacuum conditions and placing them as potential candidates for space applications while supressing liquid lubricants and the associated drawbacks. This research work focuses on analyzing the tribological performance of a hydrogenated DLC thin film coating containing 36% of hydrogen, deposited by Plasma-Enhanced Chemical Vapor Deposition (PECVD) onto AISI 52100 (100Cr6) steel discs under air and vacuum conditions. Under vacuum conditions, the coating exhibited a coefficient of friction between 0.02 and 0.05, values linked with superlubricity phenomenon, attributed to phase transition from sp3 (diamond-like) to sp2 (graphite-like) in H-DLC coatings. This phenomenon is hindered in air, while wear rate is reduced as a consequence of surface passivation. Raman spectroscopy characterization, together with confocal microscopy and tribological testing confirm the formation of a self-lubricating tribofilm in both environments and highlight its influence on friction and wear performance, enhancing the knowledge about the tribological mechanisms behind DLC solid lubricants performance suitable to be used for space applications.