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W–S–N self-lubricant coatings were deposited by d.c. reactive magnetron sputtering at two total discharge pressures of 0.6 and 1.2 Pa. The nitrogen content and S/W ratio varied from 0 to 30 at.%, and 0.6 to 1.6, respectively. The effect of deposition conditions on chemical composition, structure and mechanical properties was studied; coatings with the most promising properties have been selected for tribological testing. Coatings were nanostructured with nanograins of tungsten disulfide; the size of which decreased with increasing nitrogen content. Hardness increased with N content up to 7 GPa for coating deposited with a discharge pressure of 1.2 Pa; coatings deposited at lower pressure exhibited hardness around 9 GPa. Friction and wear behavior in humid air and dry nitrogen was evaluated using a pin-on-disk tribometer. The wear tracks and the ball wear scars were analyzed by Raman spectroscopy and scanning electron microscopy. Although the friction coefficient in dry nitrogen was significantly lower than in humid air, the wear rate was similar for both environments. Detailed wear track surface analysis showed that the tribolayer formed on the surface contained mostly tungsten disulfide and tungsten oxide. [ABSTRACT FROM AUTHOR]

ABSTRACT Carbon-based coatings with different W contents were deposited by direct current magnetron sputtering in reactive and non-reactive atmospheres. All deposited coatings have compact morphologies with amorphous (tungsten-free) or nanocrystalline structures (tungsten-doped). The latter one was indicated by very broad peaks in X-ray Diffraction spectra in the position of tungsten carbide suggesting W-carbide nanoparticles embedded in an amorphous carbon matrix. The hardness increased from 10 to 15 GPa with increasing W content. The coatings were tribological tested at dry and lubricated conditions with increasing temperature in a coating/steel configuration. In dry sliding, the friction coefficient increases with the increase of the temperature reaching values higher than 1.0. The friction is significantly lower in lubricated contact using three different oils: poly-alpha-olefin, paraffin and olive oil. The olive oil shows promising lubricating properties at the temperature lower than 70°C; however, at higher temperature, the coatings were quickly worn through. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Transition metal dichalcogenides (TMD) are well known for their self lubricant properties, due to unique crystal structure, with low hardness which makes them inappropriate in applications requiring high load bearing capacity. Nevertheless, there is still a considerable potential for further improvements since other TMDs such as diselenides remain almost unknown. The WSeC coatings were deposited by either co-sputtering from WSe2 and C targets or by working in reactive mode in an Ar+CH4 atmosphere. Carbon content varied from 25at.% up to 70at.%, Se/W ratio of co-sputtered coatings was between 0.9 and 1.0, with no significant influence of the carbon content on their variations, while in the reactive process it reached values higher than 1.7. The hardness of the coatings was evaluated by nanoindentation, with values between 1.6 and 5.6GPa. The structure of the coatings was analysed by X-ray diffraction in glancing mode, showing that the coatings have a quasi-amorphous structure. Finally, the selected samples were tested on pin-on-disc showing low friction properties of WSeC co-sputtered coatings. [Copyright &y& Elsevier]

W–S–C thin films were deposited by magnetron sputtering in a semi-industrial deposition unit. Various parameters like the composition, crystallinity, morphology and hardness were studied. A single coating was selected for tribological studies in different testing environments. The tribological response during ambient air testing was governed mainly by carbon-based phase at low normal loads and both carbon-based and WS 2 rich tribofilms at higher loads. Very low coefficients of friction (~0.01) were obtained during testing at elevated temperature due to accelerated formation of WS 2 rich tribofilms. The tribological response in a vacuum against a steel-based counterbody was unsatisfactory due to the presence of a carbon-phase at the sliding interface. Discrepancies were observed between the tribological response in dry N 2 and vacuum environments. • Self-lubricant W–S–C coatings were deposited by magnetron sputtering in a semi-industrial unit. • The composition was affected by the target to substrate distance, the power applied to the targets and substrate bias. • Good tribological performance was observed during testing at RT and elevated temperatures up to 400 °C. • Coating both counterbodies can greatly improve the tribological performance in a vacuum environment. [ABSTRACT FROM AUTHOR]

Mo-Se-C is a very less explored subset of carbon-based transition metal dichalcogenide (TMD-C) nanocomposite coatings but a potential candidate as solid lubricant coatings in aerospace and automotive industries due to excellent frictional stability both in humid air and vacuum conditions. The present work aims at the development and investigation of dc magnetron co-sputtered Mo-Se-C coatings using separate C and MoSe 2 targets, as a first step for industrial up-scaling. By varying the applied C power, a carbon content of 44 to 60 at. % was achieved. 50 at. % C was selected for the deposition of coatings with negative substrate bias of 50, 70 and 90 V dc voltage and, for the latter, pulsed dc bias was also applied. Maximum Se/Mo ratio of 1.88 was evaluated by wavelength dispersive spectroscopy (WDS) analysis. After the application of substrate bias, the deposition rate and Se/Mo ratio decreased while higher compactness was observed by scanning electron microscopy (SEM). Mo-Se-C coatings displayed broad amorphous grazing incidence X-ray diffraction patterns. Transmission electron microscopy (TEM) showed MoSe 2 platelets randomly oriented in amorphous carbon matrix. X-ray photoelectron spectroscopy (XPS) was not conclusive towards the presence of Mo-C bonds while Raman analysis showed the presence of MoSe 2 crystalline peaks. Nano-indentation tests showed an increase in the hardness of coatings deposited under negative substrate bias. Tribological tests were performed in humid air and dry nitrogen. 400C(90V) coating displayed the highest frictional stability in both environments, while the lowest friction coefficient of 0.025 and specific wear rate of 2.4 × 10-8 mm3/Nm were achieved for tests in dry nitrogen. • Effects of C power and application of substrate bias on the Mo-Se-C nanocomposite coatings deposited by DCMS were investigated. • Combination of MoSe 2 with C led to compactness, amorphousness and mechanical property enhancement as compared to pure MoSe 2 coatings. • Substrate bias resulted in highly compact and non-stochiometric coatings. • MoSe 2 nano-platelets were always present in amorphous C matrix, leading to excellent tribological properties. • Mo-Se-C coatings displayed promising compositional, structural, mechanical and sliding properties. [ABSTRACT FROM AUTHOR]