Tribological and chemical effects of long term humid air exposure on sputter-deposited nanocomposite MoS2 coatings

Lince, Jeffrey R.; Loewenthal, S. H.; Clark, Charles S.

doi:10.1016/j.wear.2019.202935

Cited by 32 publications

(39 citation statements)

References 22 publications

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“…For example, the work function of MoO 3 is typically 2 eV higher than that of MoS 2 , well above the measured increase of 0.1-0.25 eV observed in the wear scars in our experiments. It is unlikely that there is an appreciable amount of oxidation at the surface of the wear scar [45], and it is more likely to find MoO 3 in the surrounding as-deposited film, but as others have shown, these films do not typically undergo appreciable oxidation during storage in dry N 2 [38]. Lastly, adsorbates are not thought to play an appreciable role in our results, as PEEM was performed in UHV and KPFM in lab air, and results from both are in good agreement.…”

Section: Discussionmentioning

confidence: 99%

“…Interactions between water molecules and unterminated edges of MoS 2 lamellae have also been suggested as an impediment to low-strength shear [33]. In macroscale contacts, edges of MoS 2 lamellae at the surface are likely oxidized prior to testing, further enhancing interactions with water [15,24,[38][39][40]. Previous work by our group showed that the surface microstructure (i.e., crystallite or lamellae size and thickness of the oriented layer) has a significant impact on friction behavior and its evolution in the presence of various vapor species, including water and molecular oxygen.…”

Section: Introductionmentioning

confidence: 99%

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Structurally Driven Environmental Degradation of Friction in MoS2 Films

et al. 2021

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We report an investigation of the friction mechanisms of MoS2 thin films under changing environments and contact conditions using a variety of computational and experimental techniques. Molecular dynamics simulations were used to study the effects of water and molecular oxygen on friction and bonding of MoS2 lamellae during initial sliding. Characterization via photoelectron emission microscopy (PEEM) and Kelvin probe force microscopy (KPFM) were used to determine work function changes in shear modified material within the top few nanometers of MoS2 wear scars. The work function was shown to change with contact conditions and environment, and shown by density functional theory (DFT) calculations and literature reports to be correlated with lamellae size and thickness of the basally oriented surface layer. Results from nanoscale simulations and macroscale experiments suggest that the evolution of the friction behavior of MoS2 is linked primarily to the formation or inhibition of a basally oriented, molecularly thin surface film with long-range order.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Structurally Driven Environmental Degradation of Friction in MoS2 Films

et al. 2021

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“…These oxide films are usually a few nanometers thick and wear off easily, and therefore, exposing the underlying unoxidized MoS 2 films improves overall tribological performance with time. Thus, it was concluded that adsorption of water molecules reduces the tribological performance of MoS 2 films compared with the oxidation of a solid film [ 106 , 107 ]. Prasad et al, investigated the quality of the WS 2 transfer film and noted a deterioration of friction coefficient in the presence 50–60% relative humidity in the air, a trend like that of MoS 2 [ 108 ].…”

Section: Transition Metal Sulfides and Di-selenidesmentioning

confidence: 99%

Tribological Properties of 2D Materials and Composites—A Review of Recent Advances

2021

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This paper aims to provide a theoretical and experimental understanding of the importance of novel 2D materials in solid-film lubrication, along with modulating strategies adopted so far to improve their performance for spacecraft and industrial applications. The mechanisms and the underlying physics of 2D materials are reviewed with experimental results. This paper covers some of the widely investigated solid lubricants such as MoS2, graphene, and boron compounds, namely h-BN and boric acid. Solid lubricants such as black phosphorus that have gained research prominence are also discussed regarding their application as additives in polymeric materials. The effects of process conditions, film deposition parameters, and dopants concentration on friction and wear rate are discussed with a qualitative and quantitative emphasis that are supported with adequate examples and application areas and summarized in the form of graphs and tables for easy readability. The use of advanced manufacturing methods such as powder metallurgy and sintering to produce solid lubricants of superior tribological performance and the subsequent economic gain from their development as a substitute for liquid lubricant are also evaluated.

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“…Sputter-deposited nanocomposite Sb 2 O 3 -Au-MoS 2 , Sb 2 O 3 -MoS 2 , and Ni-MoS 2 coatings were tested in a POD friction/wear study conducted in nitrogen (<0.08% RH) [12]. The Sb 2 O 3 -Au-MoS 2 and Sb 2 O 3 -MoS 2 coatings were shown to greatly outperform the Ni-MoS 2 coating, by an average of 18× and 26×, respectively.…”

Section: Sputter-deposited Coatingsmentioning

confidence: 99%

“…This can prove challenging. For example, MoS 2 is an excellent solid lubricant used extensively in spacecraft applications because of its ability to lubricate effectively in vacuum and inert environments, but performs somewhat poorer when operated in air or when stored in humid air environments before launch [2,[12][13][14][15].…”

Section: Introductionmentioning

confidence: 99%

Effective Application of Solid Lubricants in Spacecraft Mechanisms

Lince¹

2020

Lubricants

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Solid lubricants, antiwear coatings, and self-lubricating composites are used in applications on spacecraft where oils and greases cannot be used because of the need to avoid lubricant volatility/migration, and where the application requires significant temperature variation, accelerated testing, higher electrical conductivity, or operation in boundary conditions. The purpose of this review is to provide spacecraft designers with tools that can aid in the effective use of solid-based tribological materials, both to increase their usage, and to reduce anomalies. The various tribological material formulations are described, including how their materials, physical, and chemical properties affect their performance. Included are typical solid lubricants like PTFE and bonded or sputter-deposited MoS2, as well as low shear metal coatings, hard coatings, and composite materials (including bulk composites and nanocomposite coatings). Guidance is given on how to develop mechanisms that meet performance requirements, but also how to optimize robustness, so that success is achieved even under unforeseen circumstances. Examples of successful applications are given, as well as how to avoid potential pitfalls, and what the future of solid tribological materials may hold.

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Tribological and chemical effects of long term humid air exposure on sputter-deposited nanocomposite MoS2 coatings

Cited by 32 publications

References 22 publications

Structurally Driven Environmental Degradation of Friction in MoS2 Films

Structurally Driven Environmental Degradation of Friction in MoS2 Films

Tribological Properties of 2D Materials and Composites—A Review of Recent Advances

Effective Application of Solid Lubricants in Spacecraft Mechanisms

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