Study of the Tribological Characteristics of Discrete Structure Coatings under Vacuum Conditions

Abstract

The study presents the results of an investigation into the tribological properties of hardening discrete coatings in vacuum, as well as composite coatings based on them with the addition of a solid lubricant layer. The subject of the research is discrete coatings based on thin TiBN films, formed by magnetron sputtering of material through photoresist masks of various geometric configurations, using explosive photolithography technology. Composite coatings were produced by magnetron deposition of a solid lubricant MoS₂ layer onto the discrete TiBN coating. The study evaluates the influence of the discrete structure geometric parameters (characteristic size of discrete elements, coating continuity, and thickness) on wear resistance and the coefficient of friction. It also examines the failure mechanisms of the investigated coatings under high contact loads in vacuum conditions. Steel plates made from 12Сr18Ni10Ti (AISI 321 equivalent) were used as substrates. The wear-resistant TiBN coatings were deposited by magnetron sputtering of a TiB target in an argon and nitrogen environment. The solid lubricant coatings were deposited by magnetron sputtering of a stoichiometric MoS₂ target in an argon environment. Tribometric tests of the coated samples were carried out using a high-vacuum tribometer equipment in a “sphere-on-flat” configuration, employing a strain gauge measurement system. Scanning electron microscopy was used to analyze the morphological features of wear tracks. Discrete TiBN coatings with characteristic element sizes ranging from 460 to 805 μm and continuity values from 0.25 to 0.7 were used in the study; the coating thickness varied from 0.88 to 2.11 μm. The results demonstrate a significant influence of the discrete structure parameters on the tribological performance. Samples with discrete elements of 700 μm in diameter, 1 μm in thickness, and 0.6 continuity showed the best wear resistance and the most stable coefficient of friction. Incorporating a solid lubricant MoS₂ layer into the discrete coating significantly reduced the coefficient of friction to the range of 0.03–0.07 and improved frictional stability during prolonged operation in vacuum. These findings confirm the promising potential of using discrete hardening coatings combined with solid lubricant layers for tribological units operating in extreme conditions. The proposed approach can be applied to extend the service life of components in vacuum and space equipment.