Promotion of running-in process by UV irradiation to CN_x coating and improvement of proof property of pressure

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The superlow friction phenomena of CN_x (Carbon Nitride) coating slid against Si3N4 ball in N2 gas was suggested to be taken place when the topmost surface of CN_x changed to graphitic structure. It was assumed that ultraviolet ray (UV) could break C-N single bond when the ray power exceeded C-N single bonding energy, and we hypothesized that UV irradiation could make the CN_x coating topmost surface graphitic without friction in N2 gas. We carried out preparing the CN_x coating irradiated UV as 254, 312, and 365 nm wave length, then these specimens were friction tested in N2 gas or ambient air to compare frictional property of with and without UV irradiation. All specimens did not show superlow friction coefficient at the initial of friction tests in N2 or ambient air, however, the coatings which were UV irradiated showed superlow friction phenomena after several friction cycles and all UV irradiated specimens showed shorter running-in period than as-deposited CN_x. The average of initial several friction cycles of as-deposited CN_x showed approximately 0.04, on the other hand, in the case of 312 nm UV irradiated CN_x showed 0.01 or lower average friction coefficient. These results indicated that UV could break the C-N single bond, these broke bonds were restructured to graphitic layer.