Mechanical and tribological properties of sputtered Mo–Se–C coatings

Transition metal dichalcogenides belong to the more developed class of materials for solid lubrication. However, the main limitation of these materials is the detrimental effect of air humidity causing an increase in the friction. In previous works, molybdenum diselenide has been shown to be a promising coating retaining low friction even in very humid environment. In this study, Mo–Se–C films were deposited by sputtering from a C target with pellets of MoSe2. Besides the evaluation of the chemical composition, the structure, the morphology, the hardness and the cohesion/adhesion, special attention was paid to the tribological characterization. The C content varied from 29 to 68 at.% which led to a progressive increase of the Se/Mo ratio. As a typical trend, the hardness increases with increasing C content. The coatings were tested at room temperature with different air humidity levels and at temperatures up to 500 °C on a pin-on-disc tribometer. The friction coefficient of Mo–Se–C coatings increased with air humidity from ∼0.04 to ∼0.12, while it was as low as 0.02 at temperature range 100–250 °C. The coatings were very sensitive to the elevated temperature being worn out at 300 °C due to adhesion problems at coating–titanium interface.