The Clarification of Low Friction Mechanism for Hydrogenated Amorphous Carbon by In-Situ Observation of Frictional Area

Abstract

Hydrogenated amorphous carbon (a-C:H) coating which is one of carbonaceous coatings shows ultra low friction coefficient (μ < 0.01) in dry Nitrogen gas. At present, it is expected to clarify low friction mechanism of a-C:H coating to apply a-C:H coating to industrial components. It was reported that hydrogen concentration, density, thickness and volume fraction of chemical bonds of surface layer (transformed layer) on bulk a-C:H coating during friction test were important to clarify low friction mechanism. But it is difficult to measure hydrogen concentration and density of transformed layer during friction test. In this study, we estimate the thickness and volume fractions of C-Csp2, C-Csp3 and C-H bond of transformed layer during friction test by reflectance spectroscopy. In addition we calculate hydrogen concentration from volume fraction of C-H bond and filling factor related to density of transformed layer during friction test. After friction test, surface energy of transformed layer is measured by sessile drop method. As a result, it is suggested that a-C:H coating shows low friction coefficient by reducing real contact area due to densification of transformed layer and repulsion force in hydrogen-terminated surface.