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To achieve the desired levels of performance and durability for bearings applied in space, a novel solid-liquid dual lubricating system was established via the WS2-MoS2 composite films sliding against oil-impregnated porous polyimide (PPI), in which polyalphaolefin (PAO) oils with different viscosities were used, respectively. The contact angle measurement indicated that the PAO oil had good wettability on the surfaces of the composite film and the PPI. The vacuum tribological behaviors of single WS2-MoS2 composite film and the dual lubricating system were mainly evaluated under different loads and speeds. In comparison with single WS2-MoS2 composite film, the dual lubricating system exhibited the low friction coefficient and synergistic lubricating effect for the low-viscosity PAO oil under severe sliding conditions. It was concluded that the cleavages of the WS2 and MoS2 crystals along the basal plane were more sufficient and formed small and thin WS2 and MoS2 platelets in the dual lubricating system. Meanwhile, it was found that oil-impregnated PPI readily released PAO lubricating oil with low viscosity, which further decreased friction on the contact interface. The lubricating mechanism of the dual lubricating system was also revealed after correlating the tribological behaviors of the different lubricating systems. [ABSTRACT FROM AUTHOR]

Abstract A novel approach by texturing the WS 2 film with the nanocone-array Ni interlayer was adopted to improve the tribological property of WS 2 film particularly prolonging the wear life for application in space. The WS 2 /Ni bilayer films were prepared by sputtering WS 2 layer onto electrodeposited Ni interlayers with different surface morphologies. The micro-structures and the tribological properties of the prepared WS 2 /Ni bilayer films were investigated. The results showed that with the existence of the nanocone-array Ni interlayer, the textured WS 2 film showed a cabbage-like structure due to the growth of the WS 2 columnar plates surrounding the Ni nanocones. The cabbage-like WS 2 /Ni bilayer thin film was benefited for improving the lubrication properties with a long wear life of 4.9 × 105 cycles while the wear life was only 0.7 × 105 cycles for the pure WS 2 and 3.2 × 105 cycles for rough Ni textured WS 2 film. The improved tribological property was mainly attributed to the reserve of the WS 2 lubricate by the Ni nanocones as well as the relative low friction coefficient of the nanocone-array Ni interlayer due to the obvious reduced real contact area. Highlights • A novel cabbage-like WS 2 /Ni bilayer film was prepared without any template. • The cabbage-like WS 2 /Ni bilayer lubricating film showed an improved lifetime. • Reservoir of the WS 2 lubricates by Ni nanocones resulted in the improved property. [ABSTRACT FROM AUTHOR]

Tribological properties and wear mechanisms of TiN films deposited by arc ion plating (AIP) against Si 3 N 4 , Al 2 O 3 and steel balls were comparatively investigated under different loads and speeds. The tribological properties of the TiN films were evidently influenced by load, speed and counterball. The different friction coefficients were related to the real contact state of the friction interface of the tribopair. The TiN films against the ceramic balls mainly were typical polishing wear, which resulted from the interaction between the preferential formation of the Ti oxide layer on the wear track surface and the small particles from ceramic balls. For steel ball, the platelets of Fe 3 O 4 adhered to the wear track surface did not generate polishing effect. [ABSTRACT FROM AUTHOR]

In the present work, WS 2 –MoS 2 nanocomposite films were sputtered, based on which solid/liquid-lubrication systems were realized by combining the WS 2 –MoS 2 films with space oils including MACs (multialkylated cyclopentanes) and CPSO (chlorinated-phenyl with methyl-terminated silicone oil). The tribological behaviors of the solid/liquid systems were investigated in vacuum. It was revealed that in comparison to pure WS 2 film, the WS 2 –MoS 2 composite film exhibited an enhanced tribological performance. Moreover, our results identified that the WS 2 –MoS 2 /MACs system integrated better the advantages of the solid and liquid lubrications and thereby a synergistic lubricating effect was generated. A tribological model was established to explain the synergistic lubricating mechanism. [ABSTRACT FROM AUTHOR]

Ag films, deposited by arc ion plating, had been exposed for 43.5 h in real low earth orbit (LEO) space environment by a space environment exposure device (SEED) aboard the China Shenzhou-7 manned spaceship. The structure, morphology, composition and tribological property of the Ag films after the space environment exposure (SEE) were investigated using X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), X-ray photoelectron spectroscope (XPS) and ball-on-disk tribometer, respectively. Depth XPS and XRD analysis revealed that after the SEE, the surface layer of Ag films was partially oxidized to Ag 2 O, the cracking and flaking phenomena could be observed from the film surface by FESEM, and so the Ag films lose its metallic shine and became gray. As a result, the tribological performance was deteriorated and the high/unstable friction was obtained. [ABSTRACT FROM AUTHOR]

MoS 2 -Cr 3 O 4 composite films were prepared by the combination method of PVD and liquid phase synthesis. The microstructure and tribological properties of films have been investigated. The results indicate that the size of Cr 3 O 4 varied from 5 nm to 500 nm and the shape of Cr 3 O 4 changed from nanospheres to nanorods by adjusting concentration of CrCl 3. The MoS 2 -Cr 3 O 4 composite films developed excellent wear resistance and much lower friction coefficient than sputtered MoS 2 both in vacuum and 45%RH air. During friction, the Cr 3 O 4 @MoS 2 core-shell structure with Cr 3 O 4 core of high hardness and soft MoS 2 shells were formed and played the role of nano-bearing, which reduced the friction and wear of the composite film. Besides, better oxidation resistance and tribological property of the MoS 2 -Cr 3 O 4 composite films in humid air were attributed to the Cr 3 O 4 nanoparticles, which occupied the most of dangling bond sites. Unlabelled Image • Cr 3 O 4 nano-particles are connected to dangling bonds of the sputtered MoS 2 film. • Occupied dangling bonds by Cr 3 O 4 can much improved the antioxidant of MoS 2 film. • The Cr 3 O 4 @MoS 2 core-shell structure formed and played a role of nano-bearing. • The Cr 3 O 4 greatly improves tribological properties of films both in air and vacuum. [ABSTRACT FROM AUTHOR]