Microstructures, mechanical properties and tribological behaviors of amorphous carbon coatings in-situ grown on polycarbonate surfaces

Abstract Pure amorphous carbon (a-C) coating, chromium doped amorphous carbon (a-C/Cr) coating and silicon doped amorphous carbon (a-C/Si) coating were synthesized on Polycarbonate (PC) plastic substrates by continuous treatment of different plasma combinations. Microstructures, mechanical properties and tribological behaviors of the as-presented coatings were systematically investigated. As a result, the in-situ growth mechanisms were demonstrated for all of these carbonaceous coatings. This in-situ growth meant an in-situ transformation from the polymer structure into inorganic structure from the surface or subsurface of the substrate followed by an epitaxial growth on the transformed inorganic layer. Cr and Si dopant generated a bulky microstructure, leading to a higher density of in-situ grown a-C/Cr and a-C/Si coatings than the a-C coating on PC substrates. The hardness and elastic modulus of PC substrate were significantly improved by these in-situ grown carbonaceous coatings. Pure a-C coating showed the best protective effect on PC substrate under sliding-friction condition, with scaly protection mechanism, among these different coatings. The fundamental for good protective effect of pure a-C coating on PC was the in-situ growth mechanism, which endowed reliable adhesion of hard a-C coating on soft PC substrate even if there were cracks under sliding condition.