Effect of surface morphology on the frictional behaviour of hot filament chemical vapour deposition diamond films

摘要

A novel deposition method combining the conventional hot filament chemical vapour deposition method and the polishing technique is proposed for fabricating ultra-smooth composite diamond (USCD) films onto cobalt cemented tungsten carbide substrates. SEM and AFM investigations show that the deposited USCD films have ultra-smooth and uniform surface, and their surface roughness values are measured by using an AFM and a surface profilometer as R_a∼ 59 and ∼88.8 nm, respectively. The tribological properties of USCD films are examined in comparative friction tests with a microcrystalline diamond (MCD), fine-grained diamond, and polished MCD films, and the effect of surface morphology on the friction behaviour of diamond films is highlighted. Friction tests show that the polished MCD and USCD films exhibit very low friction coefficients of approximately 0.08, 0.12, and 0.17, while dry sliding against counterfaces of alumina ceramic, ball-bearing steel, and copper materials. Intensive interactions between two surfaces of the mating parts result in gradual blunting of the sharp tips of diamond crystallites and accumulation of wear debris on the worn surface of diamond films. Adhered wear debris on the diamond films are supposed to have a significant influence on their frictional behaviour because they will cause increasing adhesive strength between the mating surfaces, and thus a higher friction coefficient for the contact.