Influences of ceramic mating balls on the tribological properties of Cr/a-C coatings with low chromium content in water lubrication

The influences of ceramic mating balls (SiC, Si3N4, Al2O3) on the tribological properties for hydrogen-free amorphous carbon (a-C) coatings and Cr/a-C coatings with low Cr content (3 at%) in water lubrication were investigated. The composition and microstructure of a-C and Cr/a-C coatings were characterized by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy, respectively, and the mechanical and water-lubricated tribological properties were investigated using nano-indenter and ball-on-disc tribo-meter. The results revealed that the sp3/sp2 ratio of the Cr/a-C coatings increased, while the hardness and water wetting contact angle for the Cr/a-C coatings decreased in comparison to those of a-C coatings. The ranking of friction coefficients for a-C/balls and Cr/a-C/balls tribopairs was μmSiC>μmSi3N4>μmAl2O3, which was determined by the interactive effects among mechanical properties, hydration reaction and contact pressure for coatings/balls tribopair. The specific wear rates of Cr/a-C coatings were slightly higher than those of a-C coatings.