Super-low Friction Mechanisms of Carbon Nitride Coatings with Adsorbed Nitrogen Gas

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Our research group had found that thin lubricious hard coatings such as amorphous carbon nitride (CNx) coating gave super-low friction (0.01 order of friction coefficient) in particular when combined with adsorbed gases of nitrogen.The purpose of this research was to analyze super-low friction mechanisms of carbon nitride coatings with adsorbed nitrogen gas. In addition, necessary coating condition and operating condition for giving such super low friction was clarified.The following results were mainly obtained.1.Sliding between CNx coating against CNx coated ball generates stable friction coefficient of about 0.01-0.02 by blowing of nitrogen gas. In such condition, wear rate of ball shows very low value of 1.13x10^<-8>mm^3/Nm.2.Optimum value of blowing nitrogen gas to generate stable and low friction coefficient is around 2.10cc/mm^2s.3.Low friction mechanism of the CNx coating by nitrogen gas is explained by two models ;(a)friction mechanism to shows about 0.1 and (b)friction mechanism to show between 0.01 and 0.1.4.On all wear scars when low friction coefficient of 0.1 is generated in this research, Raman spectra show certain structural changes, indicating the increase in the size and/or number of the sp^2 microdomain that can be considered as a very small graphitic structure. Therefore, it is considered that low friction in this system is generated by the graphitic structure, which has low shearing strength.5.Friction coefficient of CNx/CNx in particular under N_2 blow increases from 0.01 up to 0.1 by ion irradiation. Thus, it is considered that electrification on the wear surface affect on low friction mechanism of the CNx coating by nitrogen gas.