In this study, the tribological behavior and mechanism of multilayered graphite-like carbon (GLC) coating under different hydrostatic pressure (0.1 to 60 MPa) environments was investigated using a simulated deep-sea friction and wear test system. The morphology and composition of the friction interface were thoroughly characterized. The findings revealed that the friction coefficient exhibited higher values (yet all did not surpass 0.02) under conditions of elevated hydrostatic pressure or heavy load. The GLC coating mainly exhibits abrasive wear and the degree of wear intensifies with the increase of hydrostatic pressure and load. The graphitization of the friction interface and the production of silicon-based lubrication products are becoming increasingly evident. Consequently, it can be illustrated that the effect of hydrostatic pressures on the frictional performance of GLC coatings is achieved by changing the state of the frictional contact surfaces. Essentially, hydrostatic pressure modifies the real contact area of the friction pair by generating additional compressive loads, such that an increase in hydrostatic pressures has a similar effect on an increase in applied load. As the hydrostatic pressures and the applied load increase, the trend of abrasion smoothing on the surfaces of the friction pair becomes more pronounced. The graphite transfer film and silicon-based material generated during the friction process improve the lubrication performance of the friction pair, resulting in extremely low wear of the friction pair.

Considering the increasing demands for wear-resistant materials used for various frictions with dynamic sealing parts, we employed hybrid magnetron sputtering technology to fabricate Cr/a-C multilayered coatings with and without Cr-doping modification for comparison. The tribological behaviors of coatings when paired with Polyether ether ketone (PEEK) balls was focused under different friction environments evolving atmosphere, NaCl solution, olyalphaolefin (PAO) oil, and water-in-oil (W/O). The results demonstrated that the tribological properties of all friction pairs was strongly influenced by the surrounding environment. In the atmosphere and NaCl solution, the addition of Cr promoted the formation of a-C containing transfer film, thereby yielding the 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 W/O solution, both the facile reactivity of Cr and the intrinsic instability of W/O mixture accelerated the existence of Cr₂O₃, which caused the more severe wear. The current observations not only identified the tribological failure mechanism of Cr/GLC coatings with and without Cr doping modifications in conjunction with PEEK counterparts, but also addressed the importance of designing and fabrication of adaptive lubricant coatings for harsh multi-environment applications.