The synergistic mechanism between transfer layer and surface passivation of diamond-like carbon film under different gas pressure environments
The low friction behavior and mechanism of diamond-like carbon (DLC) film are studied under different gas pressure environments. The results present that DLC film against Al2O3 and steel balls shows a relatively stable friction coefficient in the air environment, but it shows an unstable and relatively low friction coefficient under gas pressure of 5 Pa. Under gas pressure of 10(-3) Pa, the DLC film fails rapidly although it achieves a short superlubricity state. With the decrease of gas pressure, the gas passivation effect on the surface of DLC film will be weaker and weaker while the formation degree of transfer layer will be more and more continuous and dense. The first-principles calculations imply that interfacial adhesion has a significant influence on the formation of tribofilms and surface wear. Further analysis shows that the low friction behavior and mechanism of DLC films in air, low vacuum (5 Pa) and high vacuum (10(-3) Pa) environment are not controlled by graphitization mechanism, but are caused by the synergistic action of transfer layer mechanism and surface passivation mechanism.