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

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.