A TRIBOLOGICAL INVESTIGATION OF THE GRAPHITE-TO-DIAMOND-LIKE BEHAVIOR OF AMORPHOUS-CARBON FILMS ION-BEAM DEPOSITED ON CERAMIC SUBSTRATES

A tribological investigation was conducted on the graphite-to-diamond-like behavior of hard carbon films produced on SiC, Si3N4 and ZrO2 substrates by ion beam deposition. Friction tests were performed on a ball-on-disk machine with pairs of various ceramic balls and disks coated with hard carbon films in dry and humid air, argon and N2. The friction coefficients of carbon films sliding against Si3N4 and sapphire balls were in the range 0.02-0.04 in N2 and argon, but were significantly higher (about 0.15) in humid air. The wear rates of ceramic disks coated with carbon films were unmeasurable, and, depending on the test environment, the wear rates of counterface ceramic balls were reduced by two to four orders of magnitude below those of balls slid against uncoated ceramic disks. Graphite disks were also tested, to obtain friction data that can help us to understand the graphite-to-diamond-like tribological behavior of carbon films. Micro laser Raman spectroscopy and scanning electron microscopy were used to analyze the structure and chemistry of worn surfaces and to elucidate the graphite- and diamond-like tribological behavior of amorphous carbon films.