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

Abstract

Solid lubricant coatings have received considerable research attention in the 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 (MoS 2 /DLC multilayer) coatings was reported to clarify the friction and wear behaviors in high vacuum condition with and without simulated lunar-dust (SLD). Compared with pure DLC or MoS 2 coatings, the multilayer coating showed excellent tribological performance with the low friction coefficient of 0.02 and the wear rate of ~6.5×10 -6 mm 3 /N•m. What is particularly interesting is that the wear volume of MoS 2 /DLC multilayer coatings with the increase of time is in accord 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, is also attributed to the formation of ridge layer as third body reservoirs and tribo-induced a composite transfer layer containing SLD nanoparticles and coating materials. IntroductionMany space-born systems involve relative motion of contacting surfaces, whose reliability is severely limited by the degradation of lubricants and excessive wear from lunar-dust. In NASA's reports, "Dust is the number one environmental problem on the moon", the dust on the lunar surface posed a surprisingly broad array of difficulties in moon probe program, such as vision obscuration, equipment clogging, radiator performance degradation, seals failing, and abrasive wear, whereas abrasive wear was mainly destruction of solid particles. 1,2 Consequently, a specific task has been set up under the exploration program to deal with the effects of lunar dust on surface wear.The tribological properties of solid lubricants such as graphite and the transition metal dichalcogenides (TMD-sulfides, selenides or tellurides of tungsten, molybdenum and niobium) are of technological interest for reducing friction in circumstances where liquid lubricants are impractical, such as in space. [3][4][5][6][7][8][9] Unfortunately, the tribological performance and lifetime of these flexible coatings under high vacuum condition with lunar-dust have greatly limited by the mechanical damage from the angular and sharp particles. Currently, diamond-like carbon (DLC) coatings are often referenced as potential candidates for space application due to their high load bearing capability, good adhesive strength, and excellent tribological properties. [10][11][12][13][14][15][16][17][18][19][20] In the pioneering work of Enke et al., hydrogenated DLC coating sliding against steel could provide much lower friction coefficient of 0.005-0.02 in a vacuum or an inert atmosphere (dry N 2 or dry Ar). 10 Carpick et al. revealed the passivation machanism of low friction and wear of ultrananocrystalline diam...

Influence of modulation periods on the tribological behavior of Si/a-C: H multilayer film

“…As is known, the composition of the sublayer which determines the interface bonding structure has a great effect on the multi-environmental lubrication performance of the film. Therefore, strongly combined carbide elements are preferential, such as metal (Ti, W, Mo, Cr), metallic compound (TiC, MoS 2 , TiN, TiO 2 ) and nonmetal sublayers (Si-F/a-C: H, Si/a-C: H) [12][13][14][15][16]. However, some of these sublayers are compositely accompanied with a complex interface, which is not easily gained and made clear of its interface.…”

A study on the tribological property of MoS2/Ti–MoS2/Si multilayer nanocomposite coating deposited by magnetron sputtering

“…12,13 MoS 2 coating could be deposited by magnetron sputtering and widely used in the dry air environment, vacuum and space eld. [14][15][16][17] However, the columnar crystal and loose structures can be easily formed during the deposition process of pure MoS 2 coating, which reduce the surface hardness and wear durability of coating. 13 Meanwhile, these structures increase the chemical activity to water vapor and oxygen of pure MoS 2 coating.…”