Abstract
Low stoichiometry, low crystallinity, low hardness and incongruencies involving the reported microstructure have limited the applicability of TMD-C (Transition metal dichalcogenides with carbon) solid-lubricant coatings. In this work, optimized Mo–Se–C coatings were deposited using confocal plasma magnetron sputtering to overcome the above-mentioned issues. Two different approaches were used; MoSe2 target powered by DC (direct current) or RF (radio frequency) magnetron sputtering. Carbon was always added by DC magnetron sputtering. Wavelength dispersive spectroscopy displayed Se/Mo stoichiometry of ~2, values higher than the literature. The Se/Mo ratio for RF-deposited coatings was lower than for their DC counterparts. Scanning electron microscopy showed that irrespective of the low carbon additions, the Mo–Se–C coatings were highly compact with no vestiges of columnar growth due to optimal bombardment of sputtered species. Application of substrate bias further improved compactness at the expense of lower Se/Mo ratio. X-ray diffraction, transmission electron microscopy, and Raman spectroscopy confirmed the presence of MoSe2 crystals, and (002) basal planes. Even very low carbon additions led to an improvement of the hardness of the coatings. The work reports a comparison between RF and DC sputtering of MoSe2 coatings with carbon and provides a guideline to optimize the composition, morphology, structure, and mechanical properties.
Highlights
Tribology is the field of science that plays a vital role in the everyday use of small machinery or large industrial setups
The sliding performance is affected by moisture as it can increase the coefficient of friction (COF) from 0.001 in dry and vacuum conditions [25]
The application of substrate bias led to a significant drop of Se/Mo ratio
Summary
Tribology is the field of science that plays a vital role in the everyday use of small machinery or large industrial setups. Solid lubricant coatings are under research for the past few decades, yet there are still many issues that need to be solved. In industries such as aerospace, automobile, tooling or power plants, the working conditions can change very frequently from very dry to a highly humid atmosphere, or from room temperatures to around 350–400 ◦ C [2]. Self-adaptive solid lubricant coatings represent a domain of smart materials with high potential. The most widely studied are the TMDs with carbon; it is an interesting combination of materials providing self-adaptive behavior in dry atmospheres and quite acceptable performance in humid conditions as well. The sliding performance is affected by moisture as it can increase the coefficient of friction (COF) from 0.001 in dry and vacuum conditions [25]
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