Cobalt‐Doped Diamond‐Like Carbon Coatings Combined With Functionalised Polymers for Enhanced Tribological Performance

ABSTRACT In recent years, doped diamond‐like carbon (DLC) coatings combined with functionalised copolymers have gained attention as a lubrication concept. While silicon‐doped DLC has been widely studied, polymer‐assisted lubrication on other doped DLC systems remains less explored. Cobalt (Co) doping is of interest because Co‐containing DLC has shown friction reduction in lubricants containing organic additives such as glycerol mono‐oleate. In this study, the tribological behaviour of Co‐DLC coatings lubricated with functionalised polymers was investigated in PAO4. Co‐DLC films with 6.6 and 10.7 at% Co were deposited on steel substrates by deep oscillation magnetron sputtering. Ball‐on‐disk tests at 80°C showed lower friction with PLMA‐ b ‐PDMAEMA than with PLMA, and the long‐term wear test indicated improved wear performance under PLMA‐b‐PDMAEMA lubrication. The disk specific wear rate ranged from 4 × 10 −9 to 6 × 10 −9 mm 3 /N m, and the wear‐track depth reached approximately 150 nm with PLMA but was at most about 20 nm with PLMA‐ b ‐PDMAEMA. SEM‐EDS indicated carbon‐rich deposits on the counterface that were consistent with transfer‐film formation reported for DLC lubricated with organic additives. These results highlight the potential of combining Co‐doped DLC with appropriately designed functionalised polymers to improve friction and wear in PAO4 under the specific conditions examined.