Abstract
Abstract Despite continuous improvements in machine elements over the past few decades, lubrication issues have impeded human exploration of the universe because single solid or liquid lubrication systems have been unable to satisfy the ever-increasing performance requirements of space tribology. In this study, we present an overview of the development of carbon-based films as protective coatings, with reference to their high hardness, low friction, and chemical inertness, and with a particular focus on diamond-like carbon (DLC) films. We also discuss the design of carbon-based solid-liquid synergy lubricating coatings with regards to their physicochemical properties and tribological performance. Solid-liquid composite coatings are fabricated via spinning liquid lubricants on solid lubricating films. Such duplex lubricating coatings are considered the most ideal lubrication choice for moving mechanical systems in space as they can overcome the drawback of adhesion and cold-welding associated with solid films under harsh space conditions and can minimize the crosslinking or chain scission of liquid lubricants under space irradiation. State of the art carbon-based solid-liquid synergy lubricating systems therefore holds great promise for space applications due to solid/liquid synergies resulting in superior qualities including excellent friction reduction and anti-wear properties as well as strong anti-irradiation capacities, thereby meeting the requirements of high reliability, high precision, high efficiency, and long lifetime for space drive mechanisms.
Highlights
Solid lubricating coatings are highly regarded in scientific and industrial communities due to their exceptional chemical inertness, high mechanical strength and hardness, and excellent friction reduction and wear resistance properties. They are primarily considered as hard protective coatings, which provide low friction and wear by minimizing abrasion, shear, and adhesion; they cannot reach the levels of long-term reliability and safe operation required for space drive mechanisms under high vacuum
Doped-diamond-like carbon (DLC) films with high radiation resistance have shown that they could be used as coatings for space applications to protect against damage from low-energy particles and UV irradiation because the deposition process of doped-DLC films can result in a multilayer structure with depth gradients of refractive indexes, which assures optimal antireflection and protective effects for space applications [45, 46]
After comparative research on the tribological properties of these composite lubricating coatings under high vacuum (~10–5 Pa), the results demonstrated that the coatings of multiply-alkylated cyclopentanes (MACs), ionic liquids (ILs) and Zdol possess excellent friction reducing and wear resistance behaviors in high vacuum because the friction coefficients and wear rates for the contact of DLC with steel were reduced to 0.02–0.05 and 1–3 orders of magnitude, respectively, compared with the contact of steel with steel
Summary
Solid lubricating coatings are highly regarded in scientific and industrial communities due to their exceptional chemical inertness, high mechanical strength and hardness, and excellent friction reduction and wear resistance properties. They are primarily considered as hard protective coatings, which provide low friction and wear by minimizing abrasion, shear, and adhesion; they cannot reach the levels of long-term reliability and safe operation required for space drive mechanisms under high vacuum,. Diamond-like carbon (DLC) films, especially DLCbased solid/liquid composite lubricating coatings, under simulated space environments with reference to their tribological performance
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