A feasible multilayer structure design for solid lubricant coatings in a lunar environment

Abstract

Solid lubricant coatings have received considerable research attention in space applications owing to their remarkably improved tribological characteristics. But their service life is seriously restricted by the harsh environment, such as high vacuum and abrasive wear. In this paper, a novel design of carbon-based multilayer (MoS₂/DLC multilayer) coatings was reported to clarify the friction and wear behavior in high vacuum conditions with and without simulated lunar-dust (SLD). Compared with pure DLC or MoS₂ coatings, the multilayer coating showed excellent tribological performance with a low friction coefficient of 0.02 and a wear rate of ∼6.5 × 10⁻⁶ mm³ N⁻¹ m⁻¹. What is particularly interesting is that the wear volume of MoS₂/DLC multilayer coatings with the increase of time is in accordance with the Archard linear law, regardless of the condition with or without SLD. Moreover, the surface morphology and composition of wear tracks and scars reveal that the long life of carbon-based multilayer coatings cannot be explained solely by excellent mechanical performance, and is also attributed to the formation of ridge layers as third body reservoirs and a tribo-induced composite transfer layer containing SLD nanoparticles and coating materials.