Structure and tribological behaviour of carbon nitride films

Abstract

Carbon nitride (β-C 3N 4) films were successfully deposited onto Si (100) and WC cermet substrates by unbalanced magnetron sputtering. Reactive deposition was performed by using a graphite target in an Ar/N 2 plasma. The films were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Single crystals of β-C 3N 4 above 200 nm in size were formed in the films. XPS measurements showed a maximum N/C ratio of 0.45 and a decreased N/C ratio after wear testing. The friction and wear properties of the films against alumina, copper, steel and the films themselves were determined with a ball-on-disc apparatus in ambient air at medium humidity. The effects of normal load (0.2–5 N) and linear speed (0.04 m s −1–0.4 m s −1) were also determined. The wear test results showed that the carbon nitride films possessed low coefficient of friction (COF) and excellent wear resistance. The COF of the films was in the range of 0.05–0.16. Films with relatively large β-C 3N 4 crystals showed even lower COFs and improved wear resistance. The wear mechanisms of carbon nitride films are discussed.