Wear-mechanism map of amorphous carbon nitride coatings sliding against silicon carbide balls in water

To understand the wear mechanism of amorphous carbon nitride coatings (a-CN_x) sliding against SiC ball in water, the influence of tribological variables such as normal load (W) and sliding speed (V) on the friction coefficients (μ) and the specific wear rates (w_s) was studied. The worn surfaces on disks and balls were observed by optical microscope (OM). The results indicate that the influence of the sliding speeds on the friction coefficients and the specific wear rates was more obvious than that of the normal loads. The friction coefficients and the specific wear rates decreased with an increase in the sliding speed, whereas with an increase in the normal loads, the friction coefficients and the specific wear rates fluctuated slightly. The specific wear rate of the a-CN_x coatings was ten times larger than that of the SiC balls. When the sliding velocity was larger than 0.1 m/s, the friction coefficient of the a-CN_x/SiC ball tribo-pair in water lubrication was smaller than 0.05 and the specific wear rates of the a-CN_x coatings and the SiC balls all were at a lowest level of 10^-8 and 10^-9 mm³/Nm. Furthermore, the specific wear rates of a-CN_x coatings and SiC balls increased linearly with friction coefficient (μ), while decreased linearly with the friction heat per unit time (μWV). To describe the friction and wear property of the a-CN_x coatings sliding against SiC balls in water at the normal loads of 3 ∼ 15 N and the sliding speeds of 0.05∼0.5 m/s, the wear-mechanism map for the a-CN_x/SiC tribo-pair in water was developed.