Regulation of Sulfur Concentration in Molybdenum Sulfide Layers for Qualitative Improvement of Tribological Properties of Nanolayer a-MoSx/a-C Coatings

Multilayered coatings consisting of alternating layers of amorphous molybdenum sulfide (a-MoSx) and diamond-like carbon (a-C)С are created using a combined method of vacuum and reactive pulsed laser deposition. The ratio of atomic concentrations x = S/Mo in the molybdenum sulfide layers is ~2 and 3, and the thickness of the layers does not exceed 12 nm. The tribological properties of the coatings are studied by sliding a steel ball over a disk under challenging conditions. Modification of coatings after tribological impact is studied using the method of Raman spectroscopy. A significant influence of the chemical composition of molybdenum sulfide layers on the friction coefficient and wear resistance of coatings at room testing temperature is established. An increase in the sulfur concentration provides a prolonged solid-lubricating effect both in humid air (friction coefficient of 0.1–0.2) and in argon (friction coefficient of 0.015) owing to the formation of a tribofilm containing a composition of 2H-MoS2 and a-C(S) nanophases. When the tribological test temperature in argon is reduced to –100°C, good antifriction characteristics are maintained, but the differences in the properties of the created coatings are less pronounced.