Enhancing tribological performance of graphene sheet-embedded carbon films on steel substrates via texture engineering and chromium doping

Abstract

Amorphous carbon (a-C) film is a promising solid lubricant coating due to its unique structure and excellent properties. However, its poor adhesion and long running-in period hinder the application in metal components. Graphene sheet-embedded carbon (GSEC) film has a significantly shorter running-in period but suffers from inferior tribological properties due to its rough surface and weak mechanical characteristics. In this study, we utilized an electron cyclotron resonance (ECR) plasma nano-surface manufacturing device to deposit GSEC films onto steel substrate surfaces. By manipulating the surface/interface texture and incorporating chromium (Cr) doping, the tribological properties of the GSEC films were improved both chemically and physically. The results demonstrated that the textured carbon film exhibited superior adhesion to the steel substrate and a wear life that was three orders of magnitude longer than the untextured GSEC film, under low normal load conditions while sliding against the GCr15-bearing steel ball. After doping the Cr into textured carbon films, there was a significant reduction in the friction coefficients, and the wear type of carbon film transformed from adhesive wear to abrasive wear. Moreover, the doped carbon films demonstrated prolonged wear lives under high normal loads. This improvement can be attributed to the formation of hard CrC nanocrystalline, which effectively reduced surface roughness and enhanced the mechanical properties of the carbon films. Notably, even under a contact pressure of 0.83 GPa, the doped carbon film maintained favorable tribological performances. These findings have extended the potential applications of carbon films on metal substrates.