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In order to clarify the ultra low friction mechanism of Carbon Nitride (CN x ) coatings under blowing dry Ar, thickness and area of transfer layers on mating surface were in-situ observed with an optical microscope during sliding against a sapphire hemisphere under blowing dry Ar. During sliding, thickness of transfer layer from CN x coating to a sapphire hemisphere increased and leaded to ultra low friction. When thickness and area of transfer layer was thick and small respectively, ultra low friction was observed. The result showed that the coefficient of friction decreased from 0.18 to 0.003 and remained constant throughout the friction test. It was confirmed the formation of a graphite-like transfer layer with Raman analysis and Auger Electron Spectroscopy (AES).

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Carbon Nitride (CNx) coating was reported to show a superlow friction coefficient when it slid against a Si 3 N 4 ball in nitrogen gas at atmospheric pressure. This superlow friction phenomenon occurred after a number of sliding cycles, in the so-called running-in period, due to the nitrogen atom desorption from the topmost CNx coating surface; its the surface became a graphite-like layer, and a transfer layer was formed on the counter material surface. However, a friction test and surface analysis should be conducted simultaneously, when detailed frictional phenomena including functional groups are observed on the topmost CNx surface. It was supposed that several functional groups were adsorbed on the topmost surface of the carbon system coating when the specimen was withdrawn from the synthesis chamber. In this study, we constructed a friction test apparatus in a FTIR analytic chamber to conduct friction tests and surface analysis without taking the friction test chamber out of the analytical chamber. The analysis results of 1500 cycles each indicated that the-OH or-NH functional group gradually increased with the number of sliding cycles. However, the group decreased suddenly as the friction coefficient decreased. Finally, these kinds of functional groups were not detected when the CNx coating showed superlow friction phenomena.