A novel carbon-based solid–liquid duplex lubricating coating with super-high tribological performance for space applications

In this paper, we presented the fabrication of a carbon-based solid–liquid duplex lubricating coatings and their tribological behaviors and synergy lubrication mechanism under high vacuum condition were investigated. The carbon-based solid–liquid lubricating coating was composed of TiC/a-C:H solid coating as a supporting layer and a liquid lubricating film of MACs (multialkylated cyclopentanes) as upper layer. The friction and wear properties of the solid–liquid duplex coating, the bare TiC/a-C:H film and the MACs-lubricated steel in high vacuum were compared using a high vacuum wear tester. The results showed that the bare TiC/a-C:H solid lubricating films sliding against steel failed quickly at high vacuum condition, while the friction coefficient of the carbon-based solid–liquid duplex coatings sliding against steel ball was kept at a relatively stable value of 0.08 in high vacuum, which was reduced by 43% when compared with MACs-lubricated steel. Moreover, the wear rate of carbon-based solid–liquid lubricating coating was about 1.5 × 10−8 mm3/Nm, which was nearly two orders of magnitude lower than that of the MoS2 duplex lubricating coating (8.3 × 10−7 mm3/Nm), and about three orders of magnitude lower than that of MACs-lubricated steel (9.27 × 10−6 mm3/Nm). The carbon-based solid–liquid synergy lubrication model was established to explain the much more stable and lower friction as well as long wear life of solid–liquid lubricating coatings. Such carbon-based solid–liquid lubricating coating systems with excellent tribological performance are considered as potential lubricating and protective surfaces for moving mechanical assemblies and tribological components for long-term service in space applications.