Cr doping modification for tribological behavior of Cr/a-C multilayer coatings against PEEK under diverse operational conditions

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.