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Formation of 2D transition metal dichalcogenides on TiC1-xAx surfaces (A=S, Se, Te): A theoretical study
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
2014 (English)In: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 29, no 2, 207-214 p.Article in journal (Refereed) Published
Abstract [en]

Using first principle density functional calculations, we study the formation of 2D transition metaldichalcogenides (TMDs) on TiC1-xAx, (A = S, Se, and Te) surfaces. We examine the structural misfits between chalcogen-containing TiC and different TMDs and demonstrate that the conditions for formation of TMDs are fulfilled in TiC1-xAx. We also demonstrate the influence of chalcogens on the cohesive properties and electronic structure of the carbides. We find that they react with W and form W-dichalcogenides. In the experimentally reported Ti–C–S nanocomposite coatings, the carbide grains are embedded in an amorphous carbon matrix. We discuss here the role ofthis matrix in the reaction. We propose that TiC1-xTex and TiC1-xSex are the favorable sources fordichalcogenide formation and suggest an alternative way to produce 2D materials in general. Furthermore, we argue that using Ti–C–Te or Ti–C–Se in nanocomposite coatings may be more advantageous for tribological applications than that of Ti–C–S.

Place, publisher, year, edition, pages
2014. Vol. 29, no 2, 207-214 p.
National Category
Condensed Matter Physics Inorganic Chemistry Materials Chemistry Tribology
Research subject
Materials Science; Chemistry with specialization in Inorganic Chemistry; Physics of Matter
Identifiers
URN: urn:nbn:se:uu:diva-213666DOI: 10.1557/jmr.2013.350ISI: 000332933800005OAI: oai:DiVA.org:uu-213666DiVA: diva2:683084
Funder
Swedish Foundation for Strategic Research Swedish Research CouncileSSENCE - An eScience CollaborationKnut and Alice Wallenberg FoundationEU, European Research Council, 247062-ASD
Available from: 2014-01-02 Created: 2014-01-02 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Triboactive Low-Friction Coatings Based on Sulfides and Carbides
Open this publication in new window or tab >>Triboactive Low-Friction Coatings Based on Sulfides and Carbides
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

For sustainable development, it is highly important to limit the loss of energy and materials in machines used for transportation, manufacturing, and other purposes. Large improvements can be achieved by reducing friction and wear in machine elements, for example by the application of coatings. This work is focused on triboactive coatings, for which the outermost layer changes in tribological contacts to form so-called tribofilms. The coatings are deposited by magnetron sputtering (a physical vapor deposition method) and thoroughly chemically and structurally characterized, often theoretically modelled, and tribologically evaluated, to study the connection between the composition, structure and tribological performance of the coatings.

Tungsten disulfide, WS2, is a layered material with the possibility of ultra-low friction. This work presents a number of nanocomposite or amorphous coatings based on WS2, which combine the low friction with improved mechanical properties. Addition of N can give amorphous coatings consisting of a network of W, S and N with N2 molecules in nanometer-sized pockets, or lead to the formation of a metastable cubic tungsten nitride. Co-deposition with C can also give amorphous coatings, or nanocomposites with WSx grains in an amorphous C-based matrix. Further increase in coating hardness is achieved by adding both C and Ti, forming titanium carbide. All the WS2-based materials can provide very low friction (down to µ<0.02) by the formation of WS2 tribofilms, but the performance is dependent on the atmosphere as O2 and H2O can be detrimental to the tribofilm functionality.

Another possibility is to form low-friction tribofilms by tribochemical reactions between the two surfaces in contact. Addition of S to TiC/a-C nanocomposite coatings leads to the formation of a metastable S-doped carbide phase, TiCxSy, from which S can be released. This enables the formation of low-friction WS2 tribofilms when a Ti-C-S coating is run against a W counter-surface. Reduced friction, at a moderate level, also occurs for steel counter-surfaces, likely due to formation of beneficial iron sulfide tribofilms.

The studied coatings, whether based on WS2 or TiC, are thus triboactive, with the ability to form low-friction tribofilms in a sliding contact.

 

 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 86 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1183
Keyword
coatings, thin films, tribology, tungsten disulfide, transition metal dichalcogenide, nanocomposite, TiC/a-C, tribofilms, PVD, XPS, HAXPES, XRD, SEM, TEM, Raman spectroscopy, nanoindentation
National Category
Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-230989 (URN)978-91-554-9041-6 (ISBN)
Public defence
2014-10-31, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2014-10-09 Created: 2014-09-02 Last updated: 2015-01-23Bibliographically approved

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Kádas, KrisztinaSundberg, JillJansson, UlfEriksson, Olle

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