Sliding Wear Characteristics of a-C:H:SiO_x Coatings

The paper presents the experimental study of the friction and wear characteristics of amorphous carbon coating containing hydrogen and SiO_x (a-C:H:SiO_x) deposited onto WC-8Co cemented carbide substrates. A 5 µm thick a-C:H:SiO_x coating was fabricated using plasma-assisted chemical vapor deposition (PACVD). The tribological properties of the a-C:H:SiO_x coating sliding in contact with WC–8Co, ZrO₂, SiC, Si₃N₄ counter bodies are examined using the ball-on-disc method at different normal loads and sliding speeds. Tribology testing shows that the minimum values of the friction coefficient (0.044) and the wear-rate (9.3 × 10⁻⁸ mm³/N·m) are observed when using a counter body made of silicon nitride at a 5 N indentation load. The load increase from 5 to 12 N raises the friction coefficient up to 0.083 and the wear-rate up to 46 × 10⁻⁸ mm³/N·m. When the sliding speed reaches its critical value, the coating friction provides the transition from sp3 hybridized to sp² hybridized and polymeric carbon, which is accompanied by the reduction in the friction coefficient. The a-C:H:SiO_x coating provides an increase in the critical sliding speed up to 50–75 mm/s, which exceeds that of nonalloyed (a-C and a-C:H) diamond-like carbon coatings as a result of doping by silicon and oxygen.