In this study, the tribological behavior and mechanism of multilayered graphite-like carbon (GLC) coatings under different hydrostatic pressures (0.1–60 MPa) were investigated via 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 coefficient of friction (COF) was greater (but did not surpass 0.02) under conditions of elevated hydrostatic pressure or heavy load. The GLC coating mainly experiences abrasive wear, and the degree of wear intensifies with increasing hydrostatic pressure and load. The graphitization of the friction interface and the production of silicon-based lubrication products are becoming increasingly evident. Consequently, the effect of hydrostatic pressure 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 pressure has a similar effect on an increase in the applied load. As the hydrostatic pressure and 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 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.