Study on the mechanism of ultra-low friction coefficient of CVD diamond in vacuum

近年来，在真空条件下对CVD金刚石与金属复合材料进行摩擦试验时，发现了低摩擦系数小于0.1的超润滑现象。这种现象不能用传统的理论来解释，因为几乎所有的材料在真空条件下都表现出很高的摩擦系数。为了弄清这一现象的机理，在空气、真空和氩气中对CVD金刚石与多种金属的组合进行了摩擦试验。本实验采用三种不同镍含量的不锈钢作为CVD金刚石的配合材料。通过对滑动表面的XPS分析，发现CVD金刚石与金属结合时，碳和氧表现出特别低的摩擦系数。结果表明，氧化膜中的氧对金刚石石墨化起催化剂作用，且在真空条件下具有较低的摩擦系数。

Recently, super-lubricity phenomenon showing low coefficient of friction of 0.1 or less were found in the friction test performed in vacuum for the combination of CVD diamond and metals. This phenomenon can't be explained by conventional theory, since almost all matals are thought to be show high coefficient of friction under vacuum condition. To clarify the mechanism of this phenomenon, friction tests for the combination of CVD diamond and many kinds of metals were carried out in air, vacuum, and argon. In this experiment, three types of stainless steels with different Ni contents were used for mating material of CVD diamond. From the XPS analysis of sliding surfaces, carbon and oxygen was found for combination of CVD diamond and metals, which show especially low coefficient of friction. From these results, it was clarified that the oxygen in the oxide film play a role as a catalyst for graphitization of diamond, and showing a low coefficient of friction in vacuum.