It is well known that transition metal disulfides (denoted as MS2), such as molybdenum disulfide and tungsten disulfide, are widely used as solid lubricant to wing to the inter-lamellar hex- agonal structure and inert basal planes existing in the individual crystallites where shear occurs easily. During the last few decades, the MS2 films deposited by sputtering technique have been intensively studied and widely applied for moving parts in vacuum. However , the easy reaction of unsaturated and dangling bonds of crystal MS2 with the moisture is inclined to result in degradation of tribological performance of these films. For this reason ,many proposals had been made in the literature to improve the tribological properties of MoS2 or WS2 films, mainly including nanocomposites and multilayer constructions. The results from related works revealed that the tribological performances of MoS2 or WS2 films in dry and even in humid atmosphere can be obviously improved by multilayer and nanocomposite architectures. Despite all this, the performance of the present materials still can not satisfy there quirements absolutely for future long-term space exploration,e.g.higher reliability and durability ,extreme environments and harsh working conditions. NASA report also pointed out that there is no solid lubricants and films currently exist could completely meet those demands. Recently , a novel lubrication technology ,combining solid and liquid lubricants on friction interfaces ,or namely duplex lubrication systems , shows excellent applying potential for some applications with increasingly demands.It is found that proper ombination of solid and liquid lubricants may trigger a significant improvement of the tribological performances in comparison with the single lubricant. Some results given in the papers by Erdemir et al .indicated that Ag/polyester synthetic oil solid/liquid system exhibits good capability in controlling friction and wear for both ceramic and metallic friction pairs .The tribological properties of DLC-based solid/liquid duplex lubrication systems had been systematically studied in vacuum circumstance in works by Liu et al. The results revealed that some of DLC-baseds olid–liquid systems ,such as DLC/IL,DLC/IL/Graphene and DLC/MACs systems,exhibit promising application prospectin space which mainly attribute to the substantial load- bearing capability of DLC film and good lubricity from liquid lubricant.
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