Synthesis, microstructural and mechanical properties of self-lubricating Mo-Se-C coatings deposited by closed-field unbalanced magnetron sputtering

• Published in: Surface & coatings technology 2020-07, Vol.394, p.125889, Article 125889
• Main Authors: Vuchkov, Todor, Yaqub, Talha Bin, Evaristo, Manuel, Cavaleiro, Albano
• Format: Article
• Language: English
• Subjects: Alloying; Bias; Carbon; Coatings; Coefficient of friction; Crystallites; Deposition; Friction; Friction reduction; High temperature; Lubricants; Magnetic properties; Magnetron sputtering; Mechanical properties; Molybdenum; Morphology; Nanocomposites; Nanoindentation; Selenium; Self lubrication; Self-lubricant; Substrates; Transition metal alloys; Transition metal compounds; Transition metal dichalcogenides; Tribology; Unbalance; Wear rate
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2020.125889

Carbon alloyed transition metal dichalcogenide (TMD) coatings have attracted attention in the field of tribology due to their ability to provide friction and wear reduction in diverse operating environments. This study is devoted to the up-scaling of the deposition process for self-lubricant molybdenum-selenium-carbon (Mo-Se-C) coatings. For this purpose, Mo-Se-C nanocomposite coatings are deposited by closed-field unbalanced magnetron sputtering in a semi-industrial deposition unit. The effect of the addition of carbon to sputtered MoSex coatings, the usage of negative substrate bias, and the target-to-substrate distance are studied. The carbon addition significantly improves the compactness and the mechanical properties of the pure MoSex coatings. An additional improvement is achieved by the usage of negative substrate bias during the deposition. The optimized coatings have featureless cross-sectional morphology and amorphous X-ray diffraction structure. Transmission electron microscopy reveals the presence of nanosized crystallites of MoSe2 enclosed in an amorphous carbon matrix. The hardness, measured through nanoindentation, is ~7–8 GPa for the coatings having C content of ~50 at.%, and a compact morphology. The best tribological properties for reciprocating pin-on-disk testing are characterized by coefficients of friction of 0.08–0.09 in ambient air conditions and 0.04–0.06 in dry N2 environment and elevated temperature (200 °C). The lowest specific wear rates were 2–3 × 10−7 mm3/Nm during sliding in ambient air and under dry N2, with higher values of 7–10 × 10−7 mm3/Nm during testing at elevated temperature. Mo-Se-C coatings can be upscaled for industrial production showing potential tribological properties for low friction applications. •Self-lubricant Mo-Se-C coatings were deposited by magnetron sputtering.•The target-to-substrate distance affected the Se/Mo ratio.•Usage of negative substrate bias improved the mechanical properties.•Good tribological properties were achieved during testing in different environments.