Clarification of ultra low friction phenomena of CNx coated with Ion Beam Assisted Deposition

氮化碳（CNx）涂层具有高硬度、高耐磨性和低摩擦系数等优良性能。非晶氮化碳涂层已开始用于磁性硬磁盘的涂层。基本上，a-CNx有望成为具有高硬度和耐磨性的新型涂层材料。然而，最近，我们发现CNx涂层与Si 3 N4球在氮气中的滑动表明在干燥条件下非常低的摩擦系数为0.007，即氮气起润滑作用。我们认为，这种超低摩擦在氮气中是特定的有趣的摩擦学性能的CNx。为了解CNx在氮气中的润滑机理，研究了氮气对CNx涂层与陶瓷球摩擦时的润滑作用及其润滑机理，结果表明，CNx涂层中的氮气仅对Si_3N_4陶瓷销有润滑作用。氮气压力越高，摩擦系数越低。在氮气中摩擦系数较低的情况下，接触表面上的磨损颗粒较少，sp2键增加。氮的润滑作用之一是减少滑动表面上的磨损颗粒。具有低剪切强度结合的富含sp2的结构被认为引起低摩擦。

Carbon nitride (CNx) coatings possess possibility of many attractive properties especially for high hardness, good wear durability and low friction coefficient. And amorphous carbon nitride coatings has already started to use for the coating of magnetic rigid disk. Basically, a-CNx was expected as new coating material with high hardness and wear resistance. However, recently, we found that the sliding of CNx coating against Si3N4 ball in nitrogen indicated very low friction coefficient as 0.007 under dry condition, namely nitrogen gas played a role of lubrication. We believed that such ultra low friction in nitrogen was specific interesting tribological properties of CNx. In order to know the lubrication mechanism of CNx in nitrogen, the lubrication effects of nitrogen gas for CNx coatings sliding against ceramic balls and mechanism of lubrication by nitrogen gas are investigated.As results, l it was shown that lubrication effects of nitrogen in CNx coating sliding against ceramics pin was only occurred for a Si3N4 pin. Higher pressure of nitrogen provided lower friction coefficient. In the case of low friction coefficient in nitrogen, there are few wear particles on the contact surfaces and an increase of sp2 bonding. One of the lubrication effects of nitrogen is the decrease of wear particles on the sliding surfaces. A sp2 rich structures which have low shear strength bonds is considered to cause low friction.