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

Abstract

The paper presents the experimental study of the friction and wear characteristics of amorphous carbon coating containing hydrogen and SiOx (a-C:H:SiOx) deposited onto WC-8Co cemented carbide substrates. A 5 µm thick a-C:H:SiOx coating was fabricated using plasma-assisted chemical vapor deposition (PACVD). The tribological properties of the a-C:H:SiOx 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:SiOx 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.