Pressure Effect on Surface Roughness of Gradient Chromium-doped Diamond-like Carbon Coatings under High Temperature

Abstract In this paper, the pressure effect of surface roughness of four gradient chromium-doped diamond-like carbon (GCD-DLC) coating is systemically studied in argon annealing and high pressure annealing under high temperature. After HIPping annealing, the surface roughness of the hydrogen-free group (GCr and GCrSi) decreased slightly. However, for the two hydrogen-containing GCD-DLC coatings (DCr and DCrSi), especially the DCr coating, the roughness increased significantly. The changes in surface roughness of the hydrogen-free group and the hydrogen-containing group after high-pressure annealing are opposite. The surface roughness of the DCr coating increased significantly after 500°C HIP annealing, which is attributed to the pores on the coating surface. Only the surface morphology of the DCr coating exhibited significant changes. Numerous voids appeared on the surface of the DCr5H coating after 500°C HIP annealing. There were significant differences in the size and shape of these voids compared to those after 500°C argon annealing. The voids on the coating after argon annealing were larger than those after HIP annealing. The formation of pores is associated with the breaking of carbon-hydrogen bonds and the subsequent release of hydrogen. This is because high pressure slows down the transformation from sp 3 carbon bonds to sp 2 carbon bonds. Simultaneously, high pressure also slows down the release of hydrogen within the coatings.