EFFECT OF TRIBOFILM FORMATION ON THE TRIBOLOGICAL PERFORMANCE OF HYDROGENATED CARBON COATINGS

Amorphous hydrogenated carbon (a-C:H) films were deposited by the r.f. plasma technique on stainless steel substrates. Pin-on-disc experimen ts were carried out over a wide range of normal loads (5-40 N) and sli ding velocities (0.1-3.0 m s(-1)) in order to study the friction and w ear performance of the coating against steel and alumina. The friction coefficient of a-C:H films against both steel and alumina pins decrea sed with increasing load and sliding velocity. On the pin wear surface , tribolayer formation was detected. The wear of the alumina pins incr eased with increasing load and sliding velocity when they contacted th e coating. However, the thick tribolayer formed on the wear surface of the steel pin protected it from excessive wear when high loads and sl iding velocities were applied. The wear surfaces were analysed by seco ndary ion mass spectroscopy and Auger electron spectroscopy. The analy ses revealed that the thick tribolayer formed on the pin wear surface mainly consisted of the oxides of the pin material. However, evidence of carbon was found in the sliding deposit formed in front of the cont act area of the pin and also in some cases on the pin wear surface. Ca rbon played an important role in the low friction behaviour although t he amount of carbon was low. It is assumed that a thin tribolayer with low shear strength, consisting of carbon species, is formed on the di sc wear surface. The coating wear increased when the normal load was i ncreased. Some transfer of pin material was observed on the coating we ar surface.