Counterpart-dependent friction and wear of hydrogenated tetrahedral amorphous carbon under ultra-high vacuum

Abstract

This study explores the tribological behavior of hydrogenated tetrahedral amorphous carbon (ta-C:H) coatings under ultra-high vacuum (UHV) conditions. The ta-C:H coatings were deposited via a filtered cathode vacuum arc, with varying hydrogen flow rates introduced during arc discharge. A ball-on-disk type vacuum tribometer was utilized to evaluate the tribological performance of those coatings against Si₃N₄ and ZrO₂ counterparts at 0.91 N and 1.81 N. The results revealed that friction and wear behavior were significantly influenced by the hydrogen content and the mating material. Highly hydrogenated ta-C:H formed low-friction smooth tribofilms on the counterparts and itself, showing stable low friction lower than 0.05. While Si₃N₄ exhibited high friction due to adhesion and cold-welding, ZrO₂ demonstrated low friction with the formation of flat tribofilms, even against low hydrogenated ta-C:H films. The reduced tangential friction also reduced wear between the two surfaces, resulting in a significantly low wear rate of less than 2 × 10⁻⁷ mm³/N·m. Therefore, ta-C:H films could be considered a viable candidate for a tribological coating, utilized in UHV environments.