2023 年 74 巻 9 号 p. 480-485
Carbon-based films such as diamond, diamond-like carbon, and carbon nitride exhibit a low coefficient of friction in the order of 0.1 or an ultra-low coefficient of friction in the order of 0.01. In addition, depending on the friction conditions, they may exhibit a high friction coefficient of 0.3 or higher. However, there are no reports explaining why carbon-based films exhibit these properties. To address this issue, the factors involved in the development of low friction coefficients in carbon-based films in dry environments are considered in this study, and eight phenomena are proposed. The basic concept is that a carbon-based film is graphitized by frictional heat in the presence of trace amounts of oxygen and/or water; which results in the generation of gases such as CO, CO2, H2, and N2, further reducing its friction coefficient. Consequently, it was possible to reasonably interpret the various frictional properties of carbon-based films, and to clarify the relationship between conditions such as the atmosphere of friction and friction properties, in relation to these eight phenomena.