Preparation of chameleon coatings for space and ambient environments

Baker, Colin; Chromik, Richard R.; Wahl, Kathryn J.; Hu, Jianjun; Voevodin, Andrey A.

doi:10.1016/j.tsf.2007.02.005

Cited by 76 publications

(38 citation statements)

References 33 publications

(42 reference statements)

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“…Doping of the pure TMD typically resulted in a hardness increase of about one order of magnitude higher and an increase in the density of the films, which are important factors contributing to to the formation of MoS 2 -rich tribolayer [36]. Our recent results summarized in [11] show that, in the case of TMD-C films, the TMD tribolayer is exclusively formed in the contact area, whereas carbon is immediately removed.…”

Section: Discussionmentioning

confidence: 86%

Complex frictional analysis of self-lubricant W-S-C/Cr coating

et al. 2012

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Transition metal dichalcogenides belong to one of the most developed class of materials for solid lubrication. However, one of the main drawbacks of most of the self-lubricating coatings is their low load-bearing capacity, particularly in terrestrial atmospheres. In our previous works, alloying thin films based on tungsten disulfide with non-metallic interstitial elements, such as carbon or nitrogen, has been studied in order to improve tribological performance in different environments.Excellent results were reached with the deposited coatings hardness, in some cases, more than one order of magnitude higher than single W-S films. 2In this work, W-S-C films were deposited with increasing Cr contents by co-sputtering chromium and composite WS 2 -C and targets. Two films were prepared with approx. 7 and 13 at.% of Cr.Alloying with chromium led to dense films with amorphous microstructure; the hardness and adhesion was improved. Sliding tests were carried out in dry and humid air using pin-on-disc with 100Cr6 steel ball as a counterpart. To analyse the sliding process, the surfaces in the contact were investigated by X-ray photoelectron spectroscopy (bonding), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy (TEM). Surface and sub-surface structural modification of the coating and composition of the transferred tribolayer are discussed in detail. High friction in humid air was attributed to the absence of well-ordered WS 2 sliding interface. On the other hand, the existence of such interface explained a very low friction observed in dry air.

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Section: Discussionmentioning

confidence: 86%

Complex frictional analysis of self-lubricant W-S-C/Cr coating

et al. 2012

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“…Tribological testing recently conducted at AFRL [7] revealed that these six coatings have similar adaptive friction behavior and endurance to nanocomposite coatings examined previously [1]. In this earlier study, a composition with 20% C and 20% MoS 2 was found optimal for friction adaptation of YSZ/Au/DLC/MoS 2 coatings.…”

Section: Resultsmentioning

confidence: 54%

In Situ Optical Tribometry Studies of Nanocomposite Coatings

et al. 2005

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Six nanocomposite coatings of yttria-stabilized zirconia, Au, diamond like carbon and MoS 2 have been studied by in situ tribometry. The coatings all had a nominal MoS 2 content of between 14 and 18 mol%, while the concentrations of the other components were varied. Steady state friction coefficients in both dry (0.04-0.05) and wet sliding conditions (0.06-0.08) were similar for all coatings. However, by in situ tribometry, wear mechanisms were found to differ depending on coating composition and test environment humidity. Friction spiking in high YSZ coatings was identified with local plowing and scoring of the track followed by an extrusion of transfer film material. Trends in coating hardness and modulus are correlated to composition and coating wear processes.

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“…The most complex of these materials contain several solid lubricating phases such as MoS 2 or WS 2 , DLC, and Ag with the aim of providing lowfriction performance in dry, humid, and high-temperature environments, respectively, as well as hard phases such as yttria-stabilized zirconia (YSZ) to improve mechanical properties. 73 of these nanocomposites clearly showed improved friction performance during cycling from low to high humidity and at elevated temperatures, 75 as well as improved wear resistance. 34,76 One would intuitively predict that cycling between these environments would quickly modify the lubricating phase.…”

Section: Rheologymentioning

confidence: 96%

Observing Interfacial Sliding Processes in Solid–Solid Contacts

Wahl¹,

Sawyer²

2008

MRS Bull.

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Directly seeing into a moving contact is a powerful approach to understanding how solid lubricants develop low-friction, long-lived interfaces. In this article, we present optical microscopy and spectroscopy approaches that can be integrated with friction monitoring instrumentation to provide real-time, in situ evaluation of solid lubrication phenomena. Importantly, these tools allow direct correlation of common tribological events (such as variations in friction and wear) with the responsible sliding-induced mechanical and chemical phenomena. We demonstrate the utility of in situ approaches with applications to a variety of thin-film solid lubricants.what is happening within the sliding solid-solid interfaces has limited both the modeling of contact processes and predictive engineering to improve the performance of sliding components.Solid lubrication of an interface requires both low, stable friction and development of low-wear conditions. A common strategy for solid lubrication is surface modification with a lubricant-containing coating. Unfortunately, because coatings are typically worn away during operation, their lifetimes are limited. This has motivated alternative strategies to resupply lubricants during operation (e.g., delivery of solid lubricant powders 1 or in situ formation of solid lubricants from the gas phase 2-7 ).Because sliding occurs in a buried interface, it is challenging to determine what materials processes are actively enabling stable performance. Similarly, unknown interfacial phenomena cause friction instabilities and debris generation to occur, and wear can go undetected. This article highlights recent advances of in situ tribology instrumentation and approaches that allow observation and quantification of the mechanical and chemical processes influencing friction and wear in solidlubricated contacts. These new approaches allow for an understanding of issues such as: What causes friction instabilities? How do chemistry and mechanics combine to provide low friction? How does varying the ambient environment change the interfacial film morphology and rheology? How do crystal structure and size influence lubricant performance?Several benefits can be obtained by performing tribological measurements in situ in the test environment. First, it simplifies the correlation between friction data and interface events. Second, it eliminates the need to remove the sample from the test environment and thus greatly reduces the risk of surface contamination. Perhaps most importantly, much of the highly speculative nature of deriving explanations for friction changes can be eliminated from direct observation of contact events in real time.

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Preparation of chameleon coatings for space and ambient environments

Cited by 76 publications

References 33 publications

Complex frictional analysis of self-lubricant W-S-C/Cr coating

Complex frictional analysis of self-lubricant W-S-C/Cr coating

In Situ Optical Tribometry Studies of Nanocomposite Coatings

Observing Interfacial Sliding Processes in Solid–Solid Contacts

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