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Influence of deposition temperature and amorphous carbon on microstructure and oxidation resistance of magnetron sputtered nanocomposite Cr-C films
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, Chemistry, Department of Chemistry - Ångström.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
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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.

Place, publisher, year, edition, pages
2014. Vol. 305, 143-153 p.
Keyword [en]
Chromium carbide, Magnetron sputtering, Nanocomposite, Deposition temperature, Carbon oxidation
National Category
Physical Chemistry Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-227992DOI: 10.1016/j.apsusc.2014.03.014ISI: 000336525400020OAI: oai:DiVA.org:uu-227992DiVA: diva2:732439
Available from: 2014-07-04 Created: 2014-07-02 Last updated: 2017-12-05
In thesis
1. Synthesis and Characterization of Amorphous Carbide-based Thin Films
Open this publication in new window or tab >>Synthesis and Characterization of Amorphous Carbide-based Thin Films
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, research on synthesis, structure and characterization of amorphous carbide-based thin films is presented. Crystalline and nanocomposite carbide films can exhibit properties such as high electrical conductivity, high hardness and low friction and wear. These properties are in many cases structure-related, and thus, within this thesis a special focus is put on how the amorphous structure influences the material properties.

Thin films within the Zr-Si-C and Cr-C-based systems have been synthesized by magnetron sputtering from elemental targets. For the Zr-Si-C system, completely amorphous films were obtained for silicon contents of 20 at.% or higher. Modeling of these films, as well as experimental results suggest that the films exhibit a network-type structure where the bond types influence the material properties. Higher hardness and resistivity were observed with high amounts of covalent Si-C bonds.

Several studies were performed in the Cr-C-based systems. Cr-C films deposited in a wide composition range and with substrate temperatures of up to 500 °C were found to be amorphous nanocomposites, consisting of amorphous chromium carbide (a-CrCx) and amorphous carbon (a-C) phases. The carbon content in the carbidic phase was determined to about 30-35 at.% for most films. The properties of the Cr-C films were very dependent of the amount of a-C phase, and both hardness and electrical resistivity decreased with increasing a-C contents. However, electrochemical analysis showed that Cr-C films deposited at higher substrate temperature and with high carbon content exhibited very high oxidation resistance. In addition, nanocomposite films containing Ag nanoparticles within an amorphous Cr-C matrix were studied in an attempt to improve the tribological properties. No such improvements were observed but the films exhibited a better contact resistance than the corresponding binary Cr-C films. Furthermore, electrochemical analyses showed that Ag nanoparticles on the surface affected the formation of a stable passive film, which would make the Cr-C/Ag films less resilient to oxidation than the pure Cr-C films.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. 63 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1239
Keyword
Amorphous, coating, thin film, nanocomposite, sputter deposition, PVD, XPS, SEM, TEM, electrical properties, mechanical properties
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-247282 (URN)978-91-554-9198-7 (ISBN)
Public defence
2015-05-08, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2015-04-16 Created: 2015-03-16 Last updated: 2015-07-07
2. Magnetron Sputtering of Nanocomposite Carbide Coatings for Electrical Contacts
Open this publication in new window or tab >>Magnetron Sputtering of Nanocomposite Carbide Coatings for Electrical Contacts
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
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:nbn:se:uu:diva-302063 (URN)978-91-554-9676-0 (ISBN)
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

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Nygren, KristianAndersson, MatildaEdström, KristinaNyholm, LeifJansson, Ulf

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