Considering the increasing demand for wear-resistant materials used for various frictions with dynamic sealing parts, we employed hybrid magnetron sputtering technology to fabricate Cr/amorphous carbon (a-C) multilayered coatings with and without Cr doping for comparison. The tribological behaviors of coatings paired with polyether ether ketone (PEEK) balls were investigated under different friction environments, including an evolving atmosphere, a NaCl solution, polyalphaolefin (PAO) oil, and water-in-oil (W/O). The results demonstrated that the tribological properties of all friction pairs were strongly influenced by the surrounding environment. In the atmosphere and in a NaCl solution, the addition of Cr promoted the formation of a-C-containing transfer films, thereby yielding stable and low friction characteristics. However, the dominant factor contributing to the tribological performance shifted from the coatings themselves to the PAO oil film with PAO medium. In the case of the W/O solution, both the facile reactivity of Cr and the intrinsic instability of the W/O mixture accelerated the presence of Cr₂O₃, which caused more severe wear. The current observations not only identified the tribological failure mechanism of Cr/a-C coatings with and without Cr doping modifications in conjunction with their PEEK counterparts but also addressed the importance of designing and fabricating adaptive lubricant coatings for harsh multi-environment applications.

Current tribocorrosion research of metallic materials and their surface protective coatings mainly focuses on their short-term properties, with test time of 0.5‒2.0 h and a sliding distance 50‒500 m, which may significantly deviate from the practical long-term service condition and thus cause a catastrophe of marine equipments. In this study, three carbon-based multilayer coatings (Ti/DLC, TiC_x/DLC, and Ti‒TiC_x/DLC) were deposited on S32750 substrates, and both short-term and long-term tribocorrosion behaviors were investigated. The experimental results indicate that the coatings substantially improve the tribocorrosion resistance of the S32750 stainless steel. During the short-term tribocorrosion test, TiC_x/DLC exhibited the best tribocorrosion resistance owing to its high hardness. During the long-term tribocorrosion test, however, Ti‒TiC_x/DLC coating indicated the best anti-tribocorrosion performance owing to its excellent fracture toughness together with high hardness. Moreover, under 5 N, Ti‒TiC_x/DLC can withstand a long-term test of more than 24 h. Additionally, under a higher load of 20 N, the Ti‒TiC_x/DLC with a corresponding sliding distance of approximately 1,728 m maintained a low friction coefficient of approximately 0.06. However, the coating was completely worn out; this is attributable to the formation of tribocorrosion products consisting of graphitized carbon and nanocrystalline Fe_xO_y.