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Magnetron Sputtering of Nanocomposite Carbide Coatings for Electrical Contacts
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.ORCID iD: 0000-0002-5516-6388
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Today’s electronic society relies on the functionality of electrical contacts. To achieve good contact properties, surface coatings are normally applied. Such coatings should ideally fulfill a combination of different properties, like high electrical conductivity, high corrosion resistance, high wear resistance and low cost. A common coating strategy is to use noble metals since these do not form insulating surface oxides. However, such coatings are expensive, have poor wear resistance and they are often applied by electroplating, which poses environmental and human health hazards.

In this thesis, nanocomposite carbide-based coatings were studied and the aim was to evaluate if they could exhibit properties that were suitable for electrical contacts. Coatings in the Cr-C, Cr-C-Ag and Nb-C systems were deposited by magnetron sputtering using research-based equipment as well as industrial-based equipment designed for high-volume production. To achieve the aim, the microstructure and composition of the coatings were characterized, whereas mechanical, tribological, electrical, electrochemical and optical properties were evaluated. A method to optically measure the amount of carbon was developed.

In the Cr-C system, a variety of deposition conditions were explored and amorphous carbide/amorphous carbon (a-C) nanocomposite coatings could be obtained at substrate temperatures up to 500 °C. The amount of a-C was highly dependent on the total carbon content. By co-sputtering with Ag, coatings comprising an amorphous carbide/carbon matrix, with embedded Ag nanoclusters, were obtained. Large numbers of Ag nanoparticles were also found on the surfaces. In the Nb-C system, nanocrystalline carbide/a-C coatings could be deposited. It was found that the nanocomposite coatings formed very thin passive films, consisting of both oxide and a-C.

The Cr-C coatings exhibited low hardness and low-friction properties. In electrochemical experiments, the Cr-C coatings exhibited high oxidation resistance. For the Cr-C-Ag coatings, the Ag nanoparticles oxidized at much lower potentials than bulk Ag. Overall, electrical contact resistances for optimized samples were close to noble metal references at low contact load. Thus, the studied coatings were found to have properties that make them suitable for electrical contact applications.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. , 74 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1417
Keyword [en]
transition metal carbide, amorphous carbon, composite, contact resistance, corrosion, friction, optical properties
National Category
Materials Chemistry Inorganic Chemistry Ceramics Nano Technology Composite Science and Engineering Corrosion Engineering
Identifiers
URN: urn:nbn:se:uu:diva-302063ISBN: 978-91-554-9676-0 (print)OAI: oai:DiVA.org:uu-302063DiVA: diva2:956274
Public defence
2016-10-14, Häggsalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2016-09-22 Created: 2016-08-29 Last updated: 2016-10-11
List of papers
1. Influence of deposition temperature and amorphous carbon on microstructure and oxidation resistance of magnetron sputtered nanocomposite Cr-C films
Open this publication in new window or tab >>Influence of deposition temperature and amorphous carbon on microstructure and oxidation resistance of magnetron sputtered nanocomposite Cr-C films
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2014 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 305, 143-153 p.Article in journal (Refereed) Published
Abstract [en]

It is known that mechanical and tribological properties of transition metal carbide films can be tailored by adding an amorphous carbon (a-C) phase, thus making them nanocomposites. This paper addresses deposition, microstructure, and for the first time oxidation resistance of magnetron sputtered nanocomposite Cr C/a-C films with emphasis on studies of both phases. By varying the deposition temperature between 20 and 700 C and alternating the film composition, it was possible to deposit amorphous, nanocomposite, and crystalline Cr C films containing about 70% C and 30% Cr, or 40% C and 60% Cr. The films deposited at temperatures below 300 degrees C were X-ray amorphous and 500 C was required to grow crystalline phases. Chronoamperometric polarization at +0.6 V vs. Ag/AgCl(sat. KG) in hot 1 mM H-2 SO4 resulted in oxidation of Cr C, yielding Cr203 and C, as well as oxidation of C. The oxidation resistance is shown to depend on the deposition temperature and the presence of the a-C phase. Physical characterization of film surfaces show that very thin C/Cr2O3/Cr C layers develop on the present material, which can be used to improve the oxidation resistance of, e.g. stainless steel electrodes. (C) 2014 Elsevier B.V. All rights reserved.

Keyword
Chromium carbide, Magnetron sputtering, Nanocomposite, Deposition temperature, Carbon oxidation
National Category
Physical Chemistry Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-227992 (URN)10.1016/j.apsusc.2014.03.014 (DOI)000336525400020 ()
Available from: 2014-07-04 Created: 2014-07-02 Last updated: 2016-08-29
2. Growth and characterization of chromium carbide films deposited by high rate reactive magnetron sputtering for electrical contact applications
Open this publication in new window or tab >>Growth and characterization of chromium carbide films deposited by high rate reactive magnetron sputtering for electrical contact applications
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2014 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 260, 326-334 p.Article in journal (Refereed) Published
Abstract [en]

Chromium carbide films with different phase contents were deposited at 126±26 °C by industrial high rate reactivemagnetron sputtering, using both direct current magnetron sputtering (DCMS) and high power impulsemagnetron sputtering (HiPIMS). Film structure and properties were studied by SEM, XRD, TEM, XPS, NRA, Raman spectroscopy, nanoindentation, unlubricated reciprocating sliding experiments, and a laboratory setup to measure electrical contact resistance. The films consisted of amorphous a-CrCy, a nanocrystalline minority phase of metastable cubic nc-CrCx, and a hydrogenated graphite-like amorphous carbon matrix (a-C:H). The DCMS and HiPIMS processes yielded films with similar phase contents and microstructures, as well as similar functional properties. Low elastic modulus, down to 66 GPa, indicated good wear properties via a hardness/elastic modulus (H/E) ratio of 0.087. Unlubricated steady-state friction coefficients down to 0.13 were obtained for films with 69 at.% carbon, while the electrical contact resistance could be reduced by two orders of magnitude by addition of a-C:H phase to purely carbidic films. The present films are promising candidates for sliding electrical contact applications.

Place, publisher, year, edition, pages
Elsevier: , 2014
Keyword
Direct current magnetron sputtering, High power impulse magnetron sputtering, Reactive sputtering, Amorphous chromium carbide, Solid lubricant, Contact resistance
National Category
Physical Chemistry Condensed Matter Physics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-240742 (URN)10.1016/j.surfcoat.2014.06.069 (DOI)000347584300045 ()
Conference
The 41st International Conference on Metallurgical Coatings and Thin Films, APR 28-MAY 02, 2014, San Diego, CA
Funder
Swedish Foundation for Strategic Research Swedish Research Council
Available from: 2015-01-08 Created: 2015-01-08 Last updated: 2016-08-29Bibliographically approved
3. Structure and properties of Cr-C/Ag films deposited by magnetron sputtering
Open this publication in new window or tab >>Structure and properties of Cr-C/Ag films deposited by magnetron sputtering
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2015 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 281, 184-192 p.Article in journal (Refereed) Published
Abstract [en]

Cr-C/Ag thin films with 0-14 at% Ag have been deposited by magnetron sputtering from elemental targets. The samples were analyzed by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) to study their structure and chemical bonding. A complex nanocomposite structure consisting of three phases; nanocrystalline Ag, amorphous CrCx and amorphous carbon is reported. The carbon content in the amorphous carbide phase was determined to be 32-33 at% C, independent of Ag content Furthermore, SEM and XPS results showed higher amounts of Ag on the surface compared to the bulk. The hardness and Young's modulus were reduced from 12 to 8 GPa and from 270 to 170 GPa, respectively, with increasing Ag content. The contact resistance was found to decrease with Ag addition, with the most Ag rich sample approaching the values of an Ag reference sample. Initial tribological tests gave friction coefficients in the range of 0.3 to 0.5, with no clear trends. Annealing tests show that the material is stable after annealing at 500 degrees C for 1 h, but not after annealing at 800 degrees C for 1 h. In combination, these results suggest that sputtered Cr-C/Ag films could be potentially applicable for electric contact applications.

Place, publisher, year, edition, pages
Elsevier, 2015
National Category
Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-247276 (URN)10.1016/j.surfcoat.2015.09.054 (DOI)000366072200024 ()
Funder
Swedish Foundation for Strategic Research , RMA11-0029Swedish Research Council, 621-2011-3492
Available from: 2015-03-16 Created: 2015-03-16 Last updated: 2016-08-29Bibliographically approved
4. The influence of nanoeffects on the oxidation of magnetron sputtered Cr-C/Ag thin films containing silver nanoparticles
Open this publication in new window or tab >>The influence of nanoeffects on the oxidation of magnetron sputtered Cr-C/Ag thin films containing silver nanoparticles
2017 (English)In: Chemelectrochem, ISSN 2196-0216, Vol. 4, no 2, 418-429 p.Article in journal (Refereed) Published
Abstract [en]

Well-controlled functionalization of carbide-based nanocomposite films with noble-metal surface nanoparticles of different sizes may lead to new materials with novel multifunctional properties. In this work, magnetron sputtering was used to deposit nanocomposite films comprising amorphous chromium carbide (a-CrCx), amorphous carbon (a-C), and a minority of silver in the form of embedded nanoclusters. Up to 510(10) surface nanoparticles per cm(2) with different size distributions were also found to be formed, owing to the diffusion of silver from the bulk of the film. The influences of these conductive nanoparticles on the electrochemical behavior of the films were investigated in dilute sulfuric acid. Although silver is a noble metal, the oxidation potential of the nanoparticles was about 0.4V more negative than the Ag+/Ag standard potential, meaning that the nanoparticles were oxidized in the Cr passive potential region. While this effect can mainly be explained by a low concentration of Ag+ in the electrolyte, the sizes of the nanoparticles and interactions with the matrix were also found to be important. Scanning electron microscopy and X-ray photoelectron spectroscopy were used to analyze the surface chemistries. As Ag can be replaced by other noble metals, the concept is of general interest for further studies.

Keyword
Nanoelectrochemistry, Noble metals, Carbides, Nanoparticles, Thin films
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-302060 (URN)10.1002/celc.201600615 (DOI)000394905900026 ()
Funder
Swedish Foundation for Strategic Research Swedish Research Council
Available from: 2016-08-29 Created: 2016-08-29 Last updated: 2017-04-25Bibliographically approved
5. Passive films on nanocomposite carbide coatings for electrical contact applications
Open this publication in new window or tab >>Passive films on nanocomposite carbide coatings for electrical contact applications
2017 (English)In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 52, no 13, 8231-8246 p.Article in journal (Refereed) Published
Abstract [en]

Nanocomposite transition metal carbide/amorphous carbon coatings (Me-C/a-C) deposited by magnetron sputtering have excellent electrical contact properties. The contact resistance can be as low as that of noble metal coatings, although it is known to vary by several orders of magnitude depending on the deposition conditions. We have investigated a nanocrystalline niobium carbide/amorphous carbon (NbC (x) /a-C:H) model system aiming to clarify factors affecting the contact resistance for this group of contact materials. For the first time, the surface chemistry is systematically studied, by angle-resolved X-ray photoelectron spectroscopy, and in extension how it can explain the contact resistance. The coatings presented a mean oxide thickness of about 1 nm, which could be grown to 8 nm by annealing. Remarkably, the contact resistances covered four orders of magnitude and were found to be exponentially dependent on the mean oxide thickness. Moreover, there is an optimum in the amount of a-C:H phase where the contact resistance drops very significantly and it is thus important to not only consider the mean oxide thickness. To explain the results, a model relying on surface chemistry and contact mechanics is presented. The lowest contact resistance of a nanocomposite matched that of a gold coating at 1 N load (vs. gold), and such performance has previously not been demonstrated for similar nanocomposite materials, highlighting their useful properties for electrical contact applications.

National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-302061 (URN)10.1007/s10853-017-1039-0 (DOI)000399422000050 ()
Funder
Swedish Foundation for Strategic Research VINNOVASwedish Research Council, VR 2011-3492
Available from: 2016-08-29 Created: 2016-08-29 Last updated: 2017-05-23Bibliographically approved
6. Optical methods to quantify amorphous carbon in carbide-based nanocomposite coatings
Open this publication in new window or tab >>Optical methods to quantify amorphous carbon in carbide-based nanocomposite coatings
(English)Article in journal (Other academic) Submitted
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-302062 (URN)
External cooperation:
Available from: 2016-08-29 Created: 2016-08-29 Last updated: 2016-08-29

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