Synthesis and Tribology of Carbide‐Derived Carbon Films

Carbide‐derived carbon (CDC) films are produced at atmospheric pressure on the surfaces of carbide‐based ceramic materials and coatings by a high‐temperature chlorination process. These nanoporous carbon films contain carbon nano‐onions and amorphous carbon, and may contain nanocrystalline diamond and graphite as well, depending on the synthesis conditions. The combination of such diverse carbon phases in one material or coating provides unique and potentially useful properties for a wide range of engineering applications. In this paper, we will present the results of a comprehensive study on the tribological behavior of these films. The friction coefficient of CDC in open air is comparable with that of graphite and is typically in the range of 0.15–0.25. However, the friction coefficients of CDC tend to decrease with decreasing humidity. In dry nitrogen, its friction coefficient is ∼0.1 or less. Such behavior is in contrast to that of crystalline graphite, which normally exhibits low friction at high humidity, but high friction at low humidity or in vacuum. The friction coefficient of CDC becomes increasingly lower under heavier loads; however, increasing sliding velocity does not seem to affect its frictional behavior significantly. Using a hydrogenation process that removes residual chlorine from the CDC film, the friction coefficients of CDC can be further lowered to values as low as 0.03. In an attempt to understand some of the underlying mechanisms, we carried out comprehensive chemical and structural studies of the sliding surfaces as well as bulk films and correlated these findings with the friction and wear behavior of CDC films.