Analysis of super-low friction mechanisms of carbon nitride in nitrogen gas lubrication and development of low frictiioon tribo-system

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In case of carbon nitride coatings, super-low friction coefficient on the order of 0.001 is achieved in sliding against itself or silicon nitride in the stream of nitrogen gas.In this study, effect of exposure condition after deposition of carbon nitride coatings and running-in process on friction properties of carbon nitride coatingssliding against itself or silicon nitride in nitrogen gas is investigated to clarify the super-low friction mechanisms and to develop low friction system with carbon nitride coatings.Furthermore, possibility of further lower friction and necessary surface conditions for stable and low friction coefficient as low as 0.03 are investigatedFollowing are main results of this research.(1) The average values of friction coefficient of carbon nitride coating sliding against silicon nitride ball in nitrogen gas condition varied from 0.003 to 0.6 by exposure condition after deposition of the carbon nitride coating.(2) When carbon nitride coatings are exposed to oxygen gas first for 100 seconds after deposition of carbon nitride coatings, and then exposed to ambient air with 40-60% RH for 30 minutes, the friction coefficient in nitrogen gas condition shows as low as 0.003.(3) By introducing 500 cycles of pre-sliding in ambient air, friction coefficient reduces from 0.07 to 0.004 and specific wear rate of ball also reduces from 1.0×10^<-7>mm^3/Nm to 1.0×10^<-10>mm^3 on sliding of carbon nitride against itself in nitrogen gas stream.(4) Friction coefficient of lower than 0.01 is observed in nitrogen gas stream by giving optimum range of 50 to 1,000 cycles of pre-sliding in ambient air.