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Magnetron sputtering of binary, ternary and multicomponent thin film borides and carbides
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.ORCID iD: 0000-0002-1019-6604
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Design of new thin film materials with improved properties and functionality is an important research field in materials science. In this thesis, I have used magnetron sputtering to deposit new thin film materials, which should combine high hardness and high ductility with other properties such as low friction or a good corrosion resistance. The films have been characterized with a range of techniques to determine the correlation between deposition parameters, microstructure and properties.

 The first part of the thesis is focussed on binary and ternary molybdenum-containing boride thin films with potential low-friction properties. It was found that the binary Mo-B films exhibited a nanocrystalline structure of ~ 16 nm large MoB2-x grains surrounded by an amorphous tissue phase. The special microstructure resulted in a very high hardness (29 ± 2 GPa), but limited ductility. An attempt to improve the ductility by formation of crystalline layered ternary borides such as Mo2BC and Mo2FeB2 failed due to difficulties to reach high deposition temperatures. However, the addition of carbon to the binary Mo-B films resulted initially in a reduced grain size of the MoB2-x grains. For carbon concentrations >23 at.%, a completely amorphous film was formed. Transmission electron microscopy (TEM) studies revealed that these films contained Mo-rich regions surrounded by a Mo-poor amorphous BCx phase and therefore best can be described an amorphous nanocomposite. The mechanical properties of the Mo-B-C films were strongly correlated to the amount of the softer amorphous BCx phase. Also the Mo-Fe-B films were amorphous with a hardness ranging from 19 to 26 GPa and a limited ductility. Tribological studies of the Mo-B, Mo-B-C and Mo-Fe-B films showed very high coefficients of friction (>0.8). Molybdenum and boron oxides were identified on the surface by Raman spectroscopy, but no indication of lubricating effects from these oxides could be observed. The results suggest that Mo-based borides have limited applications in future low-friction applications.

In the second part of the thesis, a high entropy alloy (HEA) of TiCrNbTaW was studied with and without the addition of carbon. The results showed that a HEA phase with bcc structure could be deposited in a wide composition and temperature range. Small amounts of carbon were dissolved into the bcc phase, while higher carbon contents resulted in a multicomponent carbide phase. The correlation between structure and properties were studied in detail. It was found that some of the films exhibited very high hardness combined with high ductility suggesting potential application of these materials as wear-resistant coatings. Finally, the corrosion resistance of these complex alloys were investigated in a very acidic environment. They were found to exhibit excellent corrosion resistance superior to hyper-duplex stainless steels.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. , p. 72
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1612
National Category
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-335987ISBN: 978-91-513-0188-4 (print)OAI: oai:DiVA.org:uu-335987DiVA, id: diva2:1165246
Public defence
2018-02-09, 2001, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2018-01-18 Created: 2017-12-12 Last updated: 2018-03-07
List of papers
1. Synthesis and characterization of MoB2−x thin films grown by nonreactive DC magnetron sputtering
Open this publication in new window or tab >>Synthesis and characterization of MoB2−x thin films grown by nonreactive DC magnetron sputtering
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2016 (English)In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559Article in journal (Refereed) Published
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-335983 (URN)10.1116/1.4948234 (DOI)
Available from: 2017-12-11 Created: 2017-12-11 Last updated: 2018-01-18
2. Synthesis and characterisation of Mo-B-C thin films deposited by non-reactive DC magnetron sputtering
Open this publication in new window or tab >>Synthesis and characterisation of Mo-B-C thin films deposited by non-reactive DC magnetron sputtering
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2017 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 309, p. 506-515Article in journal (Refereed) Published
Abstract [en]

Thin films in the Mo-B-C system with varying carbon content (up to 37 at.%) were deposited using non-reactive DC magnetron sputtering. The phase composition and microstructure were determined and the potential use of the films in sliding electrical contact applications was evaluated. Films with lower than 23 at.% carbon content consisted of nanocrystalline MoB2 - x grains surrounded by an amorphous tissue phase (a-B for binary, and a-BCx for ternary films). With increasing carbon content grain sizes was found to decrease (from 16 to 5 nm), and above 23 at.% carbon the films deposited at room temperature were X-ray amorphous. Scanning transmission electron microscopy and energy dispersive X-ray spectroscopy reveal that these films contain Mo-rich and Mo-poor regions, and thus are two-phase amorphous nanocomposites. Low-carbon content samples exhibited a friction coefficient against the steel counter surface of 1.1; this was reduced to 0.8 for high carbon-content films. Analysis of the tribofilm revealed formation of molybdenum oxide and amorphous carbon, however without significant lubricating effect at room temperature. Hardness and elastic modulus decrease with carbon content from similar to 29 to similar to 22 GPa and similar to 526 to similar to 326 GPa. These values give an WE ratio of 0.06 to 0.07, indicating brittle material. Resistivity was found to increase with carbon content from similar to 175 mu Omega cm for binary Mo-B to similar to 395 mu Omega cm for Mo-B-C thin film with 37 at.% of C. Therefore all the above results suggest that the Mo-B-C films are not suitable for sliding electrical contacts.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2017
Keyword
Mo-B-C, Magnetron sputtering, Films, Hard coatings, Molybdenum diboride, Nanocomposite
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-319135 (URN)10.1016/j.surfcoat.2016.12.003 (DOI)000396184400059 ()
Funder
Swedish Research Council, 621-2012-4359 622-2008-405Knut and Alice Wallenberg FoundationSwedish Foundation for Strategic Research , RMA11-0029
Available from: 2017-03-31 Created: 2017-03-31 Last updated: 2018-01-18Bibliographically approved
3. Synthesis and characterisation of nanocomposite Mo-Fe-B thin films deposited by magnetron sputtering
Open this publication in new window or tab >>Synthesis and characterisation of nanocomposite Mo-Fe-B thin films deposited by magnetron sputtering
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(English)Manuscript (preprint) (Other academic)
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-336121 (URN)
Available from: 2017-12-12 Created: 2017-12-12 Last updated: 2018-01-18
4. Magnetron sputtering of carbon-containing multicomponent alloys — A pathway to hard and ductile thin films
Open this publication in new window or tab >>Magnetron sputtering of carbon-containing multicomponent alloys — A pathway to hard and ductile thin films
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(English)Manuscript (preprint) (Other academic)
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-335986 (URN)
Available from: 2017-12-12 Created: 2017-12-12 Last updated: 2017-12-12
5. Synthesis and characterization of multicomponent (CrNbTaTiW)C films
Open this publication in new window or tab >>Synthesis and characterization of multicomponent (CrNbTaTiW)C films
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(English)Manuscript (preprint) (Other academic)
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-335985 (URN)
Available from: 2017-12-12 Created: 2017-12-12 Last updated: 2017-12-12

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