Multiscale Tribology of Solid Lubricants

A special issue of Lubricants (ISSN 2075-4442).

Deadline for manuscript submissions: closed (31 August 2023) | Viewed by 17789

Special Issue Editors


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Guest Editor
Department of Mechanical Engineering, Gonzaga University, Spokane, WA 99258, USA
Interests: polymer tribology; solid lubricants; nanotribology; atomic force microscopy

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Guest Editor
Department of Mechanical and Manufacturing Engineering, Miami University, Oxford, OH 45056, USA
Interests: nanotribology; multiscale modeling; molecular dynamics simulatons; corrosion
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Special Issue Information

Dear Colleagues,

Solid lubricants have long played a pivotal role in ensuring efficient and reliable operation of systems where the use of conventional, liquid lubricants is otherwise precluded. Often, these systems are designed for operation under extreme conditions—variable temperatures, harsh environments, and unpredictable loads and stress—or where lubricant materials must perform multifunctional roles. The diversity of applications that solid lubricants cater to is enabled, in part, by an equally diverse spectrum of available solid lubricant material chemistries, form factors and methods of application. Solid lubricant chemistries ranging from amorphous polymers, polycrystalline metals or lamellar solids, and single-atomic sheets may be used as bulk solid materials, dispersed solid lubricant additives, as well as “thin” surface coatings (down to a single atomic layer). Across the spectrum, regardless of material chemistry or end-application, solid lubricant function at the component length-scale is invariably derived from their structure at the atomic or microstructural length-scales.

This Special Issue will highlight recent advances in the development of novel solid lubricant materials, as well as advances in our understanding of mechanisms by which solid lubricant materials operate. We invite high-quality, scientific research manuscripts with either an applied focus, or manuscripts that advance basic scientific understanding of solid lubrication and solid lubricant materials, across mechanochemical length scales. We anticipate such research to highlight experimental, theoretical and/or computational studies that advance the science of solid lubrication, and enable development of next-generation solid lubricant materials for future technologies.

Dr. Harman Khare
Dr. Zhijiang (Justin) Ye
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Lubricants is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • polymer tribology
  • thin films
  • lamellar solids
  • mechanochemistry
  • nanotribology
  • superlubricity

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Published Papers (6 papers)

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Research

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14 pages, 5432 KiB  
Article
Investigation of the Hardness Development of Molybdenum Coatings under Thermal and Tribological Loading
by Bernd-Arno Behrens, Eugen Stockburger, Hendrik Wester, Gerhard Poll, Florian Pape, Dennis Konopka and Norman Heimes
Lubricants 2023, 11(7), 283; https://doi.org/10.3390/lubricants11070283 - 30 Jun 2023
Viewed by 1001
Abstract
The increasing global demand for innovative and environmentally friendly lubricants can be met through the use of solid lubricants. By switching from conventional lubricants such as various oils or grease to solid lubricants, new scopes of application can also be opened up. The [...] Read more.
The increasing global demand for innovative and environmentally friendly lubricants can be met through the use of solid lubricants. By switching from conventional lubricants such as various oils or grease to solid lubricants, new scopes of application can also be opened up. The main requirements for solid lubricants are a reduction in the coefficient of friction (CoF) and an increase in wear resistance. Due to the favourable material properties, molybdenum (Mo) coatings fulfil the tribological requirements and are therefore promising solid lubricants which can be applied via physical vapour deposition (PVD). In this work, the impact of substrate temperature on the hot hardness of deposited Mo coatings was determined. The specimen with the highest hot hardness was then tribologically examined both at the micro and nano level. Through an analysis of the wear tracks by means of nanoindentation and scanning electron microscopy (SEM), it was possible to detect the influence of the tribological load separately from that of the thermal loads. The results showed that the tribological load influenced the Mo coating by significantly increasing its hardness. This was achieved due to the work hardening of the Mo layer leading to an increase in the wear resistance of the coating. Full article
(This article belongs to the Special Issue Multiscale Tribology of Solid Lubricants)
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10 pages, 2215 KiB  
Article
Friction and Wear Reduction of Tungsten Carbide and Titanium Alloy Contacts via Graphene Nanolubricant
by Chris Goralka, Jake Bridges, Muhammad Jahan, Mark Sidebottom, Timothy Cameron, Yan Lu and Zhijiang Ye
Lubricants 2022, 10(10), 272; https://doi.org/10.3390/lubricants10100272 - 21 Oct 2022
Cited by 6 | Viewed by 2190
Abstract
The tribological behavior of graphene as an additive in a water-based nanofluid lubricant was investigated using pin-on-disk tests on titanium alloy (Ti-6Al-4V) and cemented tungsten carbide (WC–Co) contacts. The effect of graphene concentration and surface roughness was investigated. A non-monotonic trend of friction [...] Read more.
The tribological behavior of graphene as an additive in a water-based nanofluid lubricant was investigated using pin-on-disk tests on titanium alloy (Ti-6Al-4V) and cemented tungsten carbide (WC–Co) contacts. The effect of graphene concentration and surface roughness was investigated. A non-monotonic trend of friction and wear with increasing concentration was observed. An optimal graphene concentration of 0.10 wt.% was found to provide the lowest friction and wear at different surface roughnesses, with the friction, specific wear rate of the sample surface, and tip wear reduced by 29%, 37%, and 95%, respectively. The friction reduction and anti-wear performance of the nanofluids increased as the sample surface roughness increased. The non-monotonic friction and wear trends can be explained by the agglomeration of graphene around the contact zone, where too small a graphene concentration does not provide enough lubrication and too high a concentration prevents sliding owing to a large amount of agglomeration particles at the contact. The superior friction and wear performance of the graphene nanolubricants demonstrate its potential in minimum quantity lubrication (MQL) and other applications. Full article
(This article belongs to the Special Issue Multiscale Tribology of Solid Lubricants)
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18 pages, 3947 KiB  
Article
Elastohydrodynamic Lubrication of Compliant Circular Contacts near Glass-Transition Temperature
by Jiri Krupka, Krystof Dockal, Ivan Krupka and Martin Hartl
Lubricants 2022, 10(7), 155; https://doi.org/10.3390/lubricants10070155 - 13 Jul 2022
Cited by 4 | Viewed by 1751
Abstract
Lubrication of polymer materials nowadays represents a subject of interest in many engineering applications, such as bearings or gears, to utilize them in the areas where conventional metal materials have so far dominated. However, material properties of polymers are strongly dependent on temperature [...] Read more.
Lubrication of polymer materials nowadays represents a subject of interest in many engineering applications, such as bearings or gears, to utilize them in the areas where conventional metal materials have so far dominated. However, material properties of polymers are strongly dependent on temperature that delimits a lubrication process and leads to manifestations of viscoelastic behavior of polymers. An understanding of mechanisms, which are responsible for formation of film thickness near the glass-transition temperature, is necessary to prevent initialization of failure modes and to increase the durability of polymer engineering components. Optical chromatic interferometry was applied to investigate development of film thickness and changes in contact geometry of compliant circular contacts operated in the elastohydrodynamic lubrication regime (EHL). Film thickness was compared with soft EHL prediction models, differences in contact geometry were assessed and their contribution to film thickness development were evaluated. Qualitatively good agreement of experimental results of central film thickness and soft EHL predictions was observed; however, minimum film thickness shows significant discrepancies. Outcomes and findings confirm the operation of the compliant circular contact in Isoviscous-elastic regime of EHL and the main influence of temperature and load to thermomechanical response of amorphous polymer PMMA. Full article
(This article belongs to the Special Issue Multiscale Tribology of Solid Lubricants)
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16 pages, 12991 KiB  
Article
Tribological Behavior and Wear Mechanism of Ni-Nano TiO2 Composite Sintered Material at Room Temperature and 600 °C
by Adam Piasecki, Mateusz Kotkowiak, Maciej Tulinski and Adam Kubiak
Lubricants 2022, 10(6), 120; https://doi.org/10.3390/lubricants10060120 - 8 Jun 2022
Cited by 2 | Viewed by 1767
Abstract
In the present work, Ni-10 wt.%TiO2 self-lubricating composite sinters were prepared via a powder metallurgy. Commercially available powder of nickel and non-commercial nanometric titanium dioxide (approx. 30 nm size) produced by the microwave method was used. The produced sinters were characterized by [...] Read more.
In the present work, Ni-10 wt.%TiO2 self-lubricating composite sinters were prepared via a powder metallurgy. Commercially available powder of nickel and non-commercial nanometric titanium dioxide (approx. 30 nm size) produced by the microwave method was used. The produced sinters were characterized by evenly distributed TiO2 particles in a nickel matrix and a hardness of approx. 110 HV5. Pin-on-disc wear tests at room temperature and 600 °C were carried out. Light Microscopy (LM), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and X-Ray Diffraction (XRD) were used to characterize the wear mechanism of sintered materials. The coefficient of friction of the Ni-10 wt.% TiO2—Inconel®625 friction pair tested at room temperature was approx. 0.52. At the test temperature of 600 °C, the same friction pair had a friction coefficient of 0.35. The main wear mechanisms in dry friction conditions at 23 °C were cutting and ploughing. At the test temperature of 600 °C, formation of tribofilm on the surfaces of the friction pair was observed, which reduces the wear by friction. Full article
(This article belongs to the Special Issue Multiscale Tribology of Solid Lubricants)
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21 pages, 5372 KiB  
Article
Wear and the Transition from Static to Mixed Lubricated Friction of Sorption or Spreading Dominated Metal-Thermoplastic Contacts
by Christof Koplin, Harald Oehler, Olaf Praß, Bernadette Schlüter, Ingo Alig and Raimund Jaeger
Lubricants 2022, 10(5), 93; https://doi.org/10.3390/lubricants10050093 - 12 May 2022
Cited by 2 | Viewed by 1992
Abstract
Stiction, run-in wear and friction of lubricated polyoxymethylene homopolymer (POM)- and aliphatic polyamide (PA46)-steel tribosystems were investigated for mild-loaded mixed lubrication conditions with and without thermal conditioning of the polymers in the lubricant prior to testing. Macroscopic oscillatory tribometry and standard gliding experiments [...] Read more.
Stiction, run-in wear and friction of lubricated polyoxymethylene homopolymer (POM)- and aliphatic polyamide (PA46)-steel tribosystems were investigated for mild-loaded mixed lubrication conditions with and without thermal conditioning of the polymers in the lubricant prior to testing. Macroscopic oscillatory tribometry and standard gliding experiments were carried out. The hypothesis that sorption of a lubricant into a thermoplastic polymer and partial solving of the surface by the lubricant can change wear rate and friction was tested. It was found that for POM-lubricant-pairings, the tribological behavior is dominated by the sorption of the lubricant into the polymer; it is not influenced by the spreading energy. For the PA46-lubricant pairings, no mass uptake by sorption was measured, and the tribological behavior is influenced by spreading and changes in hardness due to thermal aging. For mild loading in mixed lubricated conditions, friction and wear properties seem to be primarily determined by the hardness-dependence of abrasive contact and less by adhesion or hysteretic mechanisms. Full article
(This article belongs to the Special Issue Multiscale Tribology of Solid Lubricants)
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Review

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59 pages, 7289 KiB  
Review
High-Temperature Solid Lubricants and Self-Lubricating Composites: A Critical Review
by Jia-Hu Ouyang, Yu-Feng Li, Yun-Zhuo Zhang, Ya-Ming Wang and Yu-Jin Wang
Lubricants 2022, 10(8), 177; https://doi.org/10.3390/lubricants10080177 - 7 Aug 2022
Cited by 43 | Viewed by 7925
Abstract
Solid lubricants are described as solid materials of intentionally introduced or in situ formed on contact surfaces in relative motion for the purpose of lowering friction and wear and providing protection from damage. Solid lubricants and advanced self-lubricating materials are widely used in [...] Read more.
Solid lubricants are described as solid materials of intentionally introduced or in situ formed on contact surfaces in relative motion for the purpose of lowering friction and wear and providing protection from damage. Solid lubricants and advanced self-lubricating materials are widely used in modern industries, especially in aerospace, aviation, automotive, metallurgy, materials forming, and machining industries, and have attracted great interest in lubrication applications under very severe circumstances such as elevated temperatures, heavy loads, ultrahigh vacuum, extreme radiation, strong oxidation, and chemical reactivity environments. Many efforts have been made to develop self-lubricating composites by a variety of material preparation techniques, which include powder metallurgy, physical/chemical vapor depositions, thermal spraying, electrodeposition, laser cladding, and additive manufacturing. Although several reviews on the development of high-temperature solid lubricants have been published, most of them only focus on a type of material, a specific process, or application. In this paper, a comprehensive review is provided to present the state-of-the-art progress in solid lubricants, self-lubricating composites/coatings, and their effective functions that can be used over a wide variety of environmental conditions, especially at elevated temperatures. The solid lubricants considered include representative soft metals, layered structure materials (e.g., graphite, hexagonal boron nitride, transition metallic dichalcogenides, MAX phase), chemically stable fluorides, binary or ternary metallic oxides, especially alkaline earth chromates, and sulfates, and synergistic effects from these solid lubricants. This paper also provides new insights into design considerations of environmental adaptive solid lubrication, and the challenges and potential breakthroughs are further highlighted for high-temperature solid lubrication applications. Full article
(This article belongs to the Special Issue Multiscale Tribology of Solid Lubricants)
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