Role of copper in tribological properties of hydrogenated amorphous carbon films in simulated physiological solution

The properties and tribological behaviors of a-C:H:Cu films with different copper contents in various simulated body fluids (deionized water, saline solution and bovine serum albumin solution (BSA), respectively) were studied. After copper incorporation, the unsaturated sp2-CH2 content in the film increased, resulting in declining wear resistance in deionized water. Nonetheless, as the copper content increased, the wear resistance of the a-C: H:Cu film in saline solution was enhanced compared with that in water, which was attributed to the obvious graphitization of wear debris promoted by copper. In BSA solution, copper incorporation improved the protein adsorption capacity of the film and facilitated the formation of denatured albumin with non-native beta-sheet structures during friction, significantly improving the wear resistance of the film.