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Abstract: Pure WS2 and WS2/Cu multilayer films were deposited by radio frequency sputtering method and the erosion behavior caused by moisture was studied. For the pure WS2 film, the morphology, microstructure, composition and also the tribological properties experienced substantial change upon storage in humid air environments. Depth XPS and Raman analysis showed that the pure WS2 film suffered deep oxidation due to the open structure, but the compact WS2/Cu multilayer film resisted oxidation very well. For the multilayer film, the oxidation was restricted on the surface layer owing to the protective effect of the reactive product cladding layer of W and Cu oxidation and the compact microstructure. The open lamella structure of pure WS2 film allowed moisture to diffuse into the film interior, and so the deep oxidation, evolution of structure and Fe substrate corrosion contributed to the deterioration of tribological properties. The WS2/Cu multilayer film exhibited better deep oxidation resistance even after storage for long durations in humid air environments, and accordingly still showed low and stable friction coefficient and long wear life. [Copyright &y& Elsevier]

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]

Abstract Characteristic porous microstructure causes poor wear resistances of sputtered transition metal dichalcogenides (TMDs) films that have important applications in space technology. TMDs/metal multilayer films exhibit improved microstructural and tribological properties, but which are unreliable due to the mismatch in thermal/mechanical properties between them as well as the metal sensibility to atomic oxygen (AO). In this study, MoS 2 /WS 2 nano-scale multilayer films were fabricated to improve the microstructural, mechanical, tribological and environment-adaptive properties of TMDs films. Results revealed that as compared with MoS 2 or WS 2 single-layer film, the multilayer film exhibited a dense microstructure, strong (002) texture and high hardness. Correspondingly, it showed a significantly improved wear resistance in vacuum, whose wear life was ~one order longer than those of single-layer films. Simulation tests revealed that even drastic thermal shock could not cause the delamination of multilayer film, which was observed from TMDs/metal multilayer system; and the oxidation from AO irradiation was restricted into film surface layer (≤10 nm). These results indicated that the microstructural, mechanical and tribological properties of TMDs films were significantly improved by the nano-scale multilayer design, and the fabricated multilayer film had potential applications in space technology. Graphical abstract Unlabelled Image Highlights • WS 2 /MoS 2 nano-scale multilayer film was designed and fabricated. • Porous microstructure was significantly restrained by multilayer fabrication. • Multilayered film exhibited better mechanical, wear-resistant and space-environment-resistant properties. [ABSTRACT FROM AUTHOR]

The WS2–Ag composite films were prepared by radio frequency co-sputtering method. The effects of alloying Ag content on composition, microstructure, mechanical properties and friction behaviors have been analyzed by X-ray photoelectron spectroscopy (XPS), grazing incidence X-ray diffraction (GIXRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS) and high resolution transmission electron microscope (HRTEM), scratch tester, nano-indentation tester and ball-on-disk tribo-tester. The Ag addition was in present of nanocrystalline phase in the boundary of the crystalline WS2 matrix and induced morphology change, but could not completely prevent the columnar platelets. The columnar platelet was composed of a great deal of nanocrystalline and a small amount of amorphous WS2 phase. There were no substantial variations in the hardness of the composite films when the Ag content was in the range of 0–20.3at.%. The suitable amount of Ag content was benefited for improving the film adhesive strength and wear resistance both in vacuum and humid air environment. Particularly, the composite film with 9.0at.% Ag exhibited the longest wear life (about 7.6×105 cycles in vacuum, 6.7×105 cycles in humid air) under high Hertzian contact pressure (as high as 1.0GPa). The wear mechanism was discussed in terms of the rearrangement of wear track and formation of transfer film. [ABSTRACT FROM AUTHOR]