Improvement in the tribological performances of Si3N4, SiC and WC by graphite-like carbon films under dry and water-lubricated sliding conditions

Silicon nitride (Si3N4), silicon carbide (SiC) and cemented carbide (WC) are good material candidates in the applications of water hydraulic systems and related water-lubrication fields. But high friction and severe wear would arise from the unavoidable solid–solid contact during running-in period, frequent starting/stopping due to the absence of effective water lubrication. Graphite-like carbon (GLC) films with high hardness was successfully deposited on above different ceramics to improve their durability and stability under different working conditions. The microstructure, morphology and mechanical characteristics of the as-deposited GLC films were investigated by Raman spectroscopy, scanning electron microscope (SEM), atomic force microscopy (AFM) and nano-indention tester. The tribological behaviors of GLC-coated Si3N4, SiC and WC were comparatively studied by a ball-on-disc tribo-meter when compared with un-coated ceramic substrates under both dry and water-lubricated sliding conditions. Results show that the friction coefficient of coated-GLC films kept a relatively lower value of 0.04–0.07 whereas the above three ceramic substrates demonstrated a much higher value in the range of 0.1–0.3 under both dry and water-lubricated conditions. In addition, the wear rate of Si3N4, SiC and WC substrates could be significantly reduced after the deposition of GLC films and interestingly the GLC-coated WC exhibited unique super-low wear rate (nearly non-wear properties). The tribological performance of coated-GLC films greatly depended on the ceramic substrates and the corresponding friction-reduction and anti-wear mechanisms related with different wear conditions and substrates were also revealed. Such GLC films are considered as potential protective and lubricating surfaces for water-lubricated parts such as water-lubricated bearing, mechanical seals and other moving parts used in water environment.