Tribological properties of segment-structured diamond-like carbon films

Diamond-like carbon (DLC) has been widely recognized as a tribo-coating material acting like a high wear-resistant solid lubricant with a low friction coefficient. The tribological behavior of DLC films depends on the environmental conditions, the nature of the coating, and mechanical properties of the substrate. Particularly, when the DLC film is distorted with the deformation of a soft substrate, the fragile DLC film is considerably damaged. In this study, DLC films have been deposited by RF-plasma chemical vapor deposition (CVD) with methane gas on soft-material substrates, such as rubber and aluminum, and friction and wear tests have been conducted using a ball-on-disk test. In the case of rubber substrates, DLC films show a relatively low friction coefficient from 0.2 to 0.3, despite extensive substrate deformation. Results of observation of the surface of the rubber substrate suggest that the DLC film forms a “segment structure” automatically, and a “segment structure coating” was applied to an aluminum substrate. Ball-on-disk test results revealed that wear resistance of the segment-structured DLC film was approximately twofold higher than that of a conventional continuous DLC coating.