The Effect of Sliding History on the Steady State Friction Coefficient between CNX Coatings under N2 Lubrication

In order to clarify the effect of reducing friction with N2 gas supply by blowing, friction tests were carried out with ball/disk combinations of Si3N4/Si3N4, Si3N4/CNx, CNx/Si3N4 and CNx/CNx in air, O2 gas stream and N2 gas stream. As a result, steady state friction coefficient reduced by N2 gas supply in contact combinations of Si3N4/Si3N4, Si3N4/CNx, and CNx/CNx by the amount of 50%, 50% and 77% respectively. In the cases of Si3N4/CNx and CNx/CNx sliding, sliding history before the N2 gas supply much affected the steady state friction coefficient in N2 gas stream. The initial 50 cycles sliding in O2 gas stream before N2 gas supply by blowing to the sliding interface of CNx/CNx reduced the friction coefficient to 0.005 from about 0.1 that was obtained in the same system in N2 gas stream from the 1st friction cycle. In the running-in process, friction coefficient increased in the initial stage, and decreased to relatively low and constant value. Such change in air and O2 gas stream were ten times faster than that in N2 gas stream. It was concluded that an optimum sliding cycles in air or O2 gas stream before N2 gas supply could be necessary not only to obtain low friction in N2 gas stream but also to decrease total wear.