Relation between Frictional Reducing Property and Tribo-Chemical Reaction about DLC Coating with Oleic Acid Lubrication during Sliding

Abstract

Diamond-Like Carbon (DLC) coating provides low friction properties without lubricants and, with lubricants such as organic acid, should provide ultra low friction. In this study, the friction property of two types of DLC coating, which were hydrogenated amorphous carbon (a-C:H) by the Plasma-Enhanced Chemical Vapor Deposition (PECVD) process and tetrahedral amorphous carbon (ta-C) by the T-Shaped Filtered Arc Deposition (T-FAD) process, were evaluated with oleic acid lubrication. It was found that friction coefficient of ta-C with deuterated oleic acid lubrication provided much lower than that of a-C:H. The tribo-film on wear track was analyzed by time-of-flight secondary ion mass spectrometer and X-ray photoelectron spectroscopy. As a result, it was found that larger amount of C-O and C=O bond derived from oleic acid were detected in the upper layer of tribo-film formed on the sliding surface of ta-C disc. It was suggested that difference of friction property between a-C:H and ta-C seemed to be caused by different composition of tribo-film generated during sliding.