Comparison of three types of carbon composite coatings with exceptional load-bearing capacity and high wear resistance

Surface coatings for high load wear applications require a combination of high hardness and toughness as well as good adhesion. Metal–carbon composite coatings have attracted special interest because of their low friction coefficients and low wear rates. Unlike the normal diamond-like carbon coatings which consist of a mixed sp3 and sp2 bonding structure and are usually highly stressed, a graphite-like carbon composite coating is reported, which demonstrates exceptionally high toughness and high wear resistance. This paper reports the preparation and characterization of three types of chromium–carbon composite coatings. The coating samples were deposited under different conditions using unbalanced magnetron sputtering of both chromium and graphite targets, and characterized with Raman spectroscopy, nanoindentation, scratch tests and pin-on-disc wear tests against alumina. A hydrocarbon gas (C4H10) was also used during deposition to explore the influence of a sputter-chemical vapor deposition hybrid process on coating properties. The optimisation and the deposition parameter dependence of the coating properties as well as the sliding wear performance of the coatings are discussed. The results show that (1) the coating deposited in H2/Ar atmosphere has better low load wear performance due to its higher hardness; (2) the coating deposited in pure Ar atmosphere has exceptionally high load-bearing capacity and excellent wear resistance attributed to its excellent adhesion, high toughness and low friction coefficient; (3) the coating deposited in butane/Ar atmosphere has a higher deposition rate, blacker colour and excellent high-load wear performance.