Hydrogenated amorphous carbon (a-C:H) films exhibit excellent friction properties such as high mechanical hardness, high wear resistance, and low friction. a-C:H films have amorphous structures generally composed of sp2- and sp3-hybridized carbon, which bring about extraordinary friction properties. Some reports have focused on the low-friction mechanism of a-C:H films, concluding that it is induced by the existence of graphitized wear particles at the sliding interface. It is possible to consider the existence of graphitized wear particles as the most important factor in achieving the lower friction of a-C:H films. We focus on the effects of surface texture in trapping the graphitized particles at the sliding interface and discuss the role of surface texture with regard to the friction properties of a-C:H films. Micro slurry-jet erosion (MSE) surface machining was employed to manipulate the surface texture on a high-carbon chromium-bearing steel substrate, upon which a-C:H films were deposited. The friction properties of a-C:H films deposited on a mirror-like polished substrate (a-C:H/mirror-like) and on an MSE-produced substrate (a-C:H/MSE-produced) were compared using a reciprocating-type ball-on-disk sliding tester. From the results of friction testing, it is confirmed that a-C:H/MSE-produced films indicated lower friction coefficients compared with the a-C:H/mirror-like case. Scanning electron microscopy (SEM) and Raman spectroscopy were performed to study the friction improvement mechanism of the a-C:H/MSE-produced films. SEM revealed the existence of wear particles in the wear track of a-C:H/MSE-produced films. It is confirmed by Raman spectroscopic analysis that these wear particles’ structure was changed, adopting a graphite-like structure. From these results, it is possible to consider that the existence of graphitized wear particles induced lower shearing resistance at the sliding interface, enabling friction improvement.
