Effect of a-CNx coating on tribological properties of SiC ceramic in water

The tribological behaviors of a-CN_x/SiC tribo-pairs in water at low velocity were investigated and compared with SiC/SiC at room temperature. The results showed that the mean value μ of friction coefficients at steady state for a-CN_x/SiC tribo-pairs (μ=0.075-0.12) was lower than that of SiC/SiC systems (μ=0.24-0.27). At a constant sliding speed, μ for two kinds of tribo-couples decreased with an increase in normal load, but at a constant normal load, μ for SiC/SiC system was nearly independence of sliding speed, whereas that of a-CN_x/SiC tribo-pair decreased with sliding speed. The specific wear rates (w_s) of ball and disk for a-CN _x/SiC tribo-couples were considerably reduced by a factor up to 10 in the comparison to those of SiC/SiC systems. The observations of wear scars showed that the wear mechanism of CN_x coating was micro-fracture of irregularities on the film surface for build-up of tribolayer, while that of SiC/SiC system was dominated by mechanical wear.