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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]

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]

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]

Abstract: A Ni3Al–Ag–Mo–BaF2/CaF2 self-lubricating composite coating was fabricated by a powder metallurgical process. The tribological properties of the coating against Si3N4 were investigated over a wide temperature range (25–1000°C). The results showed that the coating had a low friction coefficient (0.24–0.38) in the entire temperature range. Lubricating mechanism analysis results indicated that Ag took effect at low temperature (below 400°C); BaF2/CaF2 began to work as a solid lubricant as the temperature raised; and the molybdates, which formed by the fluorides oxidation, act as lubricants at higher temperatures (above 800°C). As a result, the coating expressed a low friction coefficient from 25°C to 1000°C. [Copyright &y& Elsevier]

Abstract: A Ni3Si–Cr7C3 composite coating was fabricated on AISI 1020 steel substrate by self-propagating high-temperature synthesis (SHS) casting route. Phase composition, microhardness and dry sliding wear behavior of the coating were studied. The results indicated that the coating was mainly consisted of Ni3Si and Cr7C3. The microhardness of coating is about 900HV. The friction and wear tests showed that although the friction coefficient had no obvious change, the wear resistance of the AISI 1020 steel matrix was improved greatly. Also, the corrosion test result showed that the coating had an excellent corrosion resistance. [Copyright &y& Elsevier]

Abstract: Ti–Al–C films were deposited on silicon (100) substrates using magnetron sputtering TiAl target and graphite target in argon atmosphere at various substrate negative bias voltages. The composition, surface morphology, hardness and friction coefficient of the resulting films were characterized using x-ray photoelectron spectroscope, energy dispersive spectrometry, atomic force microscopy, nanoindentation and tribological tester. Results show that the structure and properties of the deposited films strongly depend on the applied substrate negative bias voltage. The Ti–Al–C films deposited at high substrate negative bias voltage show high surface roughness, low hardness and short wear life. In contrast, the Ti–Al–C films deposited without negative bias voltage exhibit uniform and smooth surface, a high hardness of approximately 37 GPa and low friction coefficient and long wear life. Excellent friction and wear behaviors of the Ti–Al–C films deposited without negative bias may be attributed to the dense structure and high hardness. [Copyright &y& Elsevier]

Abstract: PTFE/PPS composite coating was prepared on stainless steel block by spraying and curing at high temperature. The hydrophobic properties and tribological performances of the coatings were measured with CA-A contact angle meter and evaluated on a ring-on-block wear tester, respectively. Moreover, the worn surfaces of the PPS composite coating and the transfer films formed on the surface of the counterpart ring were investigated by SEM and optical microscope (OM), respectively. FTIR and XPS analyses were performed to detect the element gradient-distribution and chemical changes of the PTFE/PPS composite coating. It was concluded that during the curing process, PTFE macromolecule chain shifted gradually from coating interior to the surface, resulting in fluorine (F) enrichment on the top surface. The gradient distribution of fluorine led to the possession of both good hydrophobic property and strong adhesive strength of the PTFE/PPS composite coatings. XPS analyses indicated that the high shear force led to decomposition and oxidation of the element of S in the PTFE/PPS coating; and the generated active S reacted tribochemically with counterface Fe, atmospheric O and H2O to form FeSO4 or Fe2(SO4)3. [Copyright &y& Elsevier]

Abstract: Microarc oxidation coatings on AM60B magnesium alloy were prepared in phosphate–KOH electrolytes with and without NaAlO2 addition. The effect of NaAlO2 on the characteristic of breakdown voltage in different concentrations of NaAlO2 has been studied. The compositions, structure and morphologies of the oxide coatings formed in different concentrations of NaAlO2 were determined by energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The corrosion resistance of the oxide coatings was evaluated in 3.5 wt.% NaCl solution using potentiodynamic polarization tests. The results showed that the solution conductivity increased while the values of breakdown voltage decreased with the increase of concentration of NaAlO2. In both cases the coatings contained Mg, Al, O and P as well as a trace amount of Na and K, and were mainly composed of MgO and spinel MgAl2O4. The addition of NaAlO2 into the base electrolyte resulted in the increase of spinel MgAl2O4 in the oxide coating. Furthermore, the number and size of micropores on top of the surface decreased with the increasing concentration of NaAlO2, though the surface roughness increased with the NaAlO2 addition. The coating formed in the electrolyte containing 8.0 g/L NaAlO2 exhibited the highest corrosion resistance in NaCl solution. [Copyright &y& Elsevier]