Superlubricity of CNx-coatings in nitrogen gas atmosphere

This chapter introduces CNx-coatings produced on Si-wafers or Si₃N₄ disks by having the deposition of carbon from a solid carbon target of 99.999% purity together with the mixing of nitrogen ions irradiated simultaneously from an ion beam gun. The carbon for the coating on Si-wafer is sputtered from a carbon target by argon ion, and on Si₃N₄ disk it is evaporated by heating with an electron beam. The hardness of the coating on Si-wafer is about 30 GPa in the indentation depth 10-50 nm. It is experimentally confirmed that the sliding of CNx-coating against itself or Si₃N₄ in nitrogen gas atmosphere gives the friction coefficient in the 0.005-0.01 range, and the wear rate below 10-7 mm³/Nm. The N₂ effect of reducing friction and wear is further enhanced by exposing the running-in process to O₂ or humid air. The analysis of the tribolayer formed on the wear scar by Raman shows the existence of a graphite-like structure. Therefore, the key to understanding the mechanism of low friction with CNx-coatings in nitrogen gas seems to exist in the interaction between the graphite-like structure of the tribolayer and the surrounding nitrogen.