uu.seUppsala University Publications
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Nb-B-C thin films for electrical contact applications deposited by magnetron sputtering
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
Show others and affiliations
2014 (English)In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 32, no 4, 041503- p.Article in journal (Refereed) Published
Abstract [en]

The high wear resistance, high chemical inertness, and high electrical conductivity of magnetron-sputtered transition metal diborides (MeB2) make them a candidate material for sliding electrical contacts. However, their high hardness makes it difficult to penetrate surface oxides, resulting in a high electrical contact resistance. We have in this study investigated how the contact resistance can be improved by the formation of softer Nb-B-C films. The Nb-B-C films were deposited by magnetron sputtering and shown to exhibit a nanocomposite microstructure consisting of nanocrystalline NbB2-x grains with a solid solution of C separated by an amorphous BCx phase. The formation of the BCx phase reduces the hardness from 41 GPa for the NbB2-x film to 19 GPa at 36 at.% C. As a consequence the contact resistance is drastically reduced and the lowest contact resistance of 35 mΩ (contact force 5 N) is achieved for a film containing 30 at.% C. However, crack formation and subsequent delamination and fragmentation is observed for the C-containing Nb-B-C films in tribology tests resulting in high friction values for these films.

Place, publisher, year, edition, pages
2014. Vol. 32, no 4, 041503- p.
Keyword [en]
boride, structural characterization, electrical properties, mechanical properties, friction, nanocomposite
National Category
Materials Chemistry
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-219032DOI: 10.1116/1.4875135ISI: 000338718400015OAI: oai:DiVA.org:uu-219032DiVA: diva2:698063
Available from: 2014-02-20 Created: 2014-02-20 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Synthesis and Characterization of Multifunctional Carbide- and Boride-based Thin Films
Open this publication in new window or tab >>Synthesis and Characterization of Multifunctional Carbide- and Boride-based Thin Films
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis present research on synthesis, microstructure, and properties of carbide- and boride- based thin films. The films have been synthesized by dc magnetron sputtering, and their microstructures have been characterized mainly by X-ray photoelectron spectroscopy (XPS), X-ray diffraction, and transmission electron microscopy.  One of the main objectives with this research has been to evaluate the thin films potential as materials for sliding electrical contact applications and this have influenced, which properties that have been evaluated.

Co-sputtered Nb-C films have a microstructure comprising of nanocrystalline NbCx  (nc-NbCx) grains embedded in a matrix of amorphous C (a-C). A thinner a-C matrix form in the Nb-C films compared to the well-studied Ti-C system. As a consequence, the Nb-C films have a higher hardness and conductivity than previously studied Ti-C sputtered under similar conditions. The promising electrical contact properties are attained for reactively sputtered Nb-C films under industrial conditions, at deposition rates two orders of magnitude higher. A reduction in crystallinity is seen when Si is added to the Nb-C films and amorphous films forms at Si content > 25 at.%. The alloying of Si was however not beneficial for the electrical contact properties.

Substoichiometric CrB2-x (B/Cr = 1.5) and NbB2-x (B/Nb = 1.8) films are achieved when deposited from MeB2 targets. Boron segregates to grain boundaries forming a B-rich tissue phase. This result in superhardness for the NbB2-x films (42 ± 4 GPa) as well as a low friction attributed to the formation of a boric acid film. Carbon forms a solid solution in the MeB2 grains as well as segregating to grain boundaries forming an amorphous BCx (a-BCx) phase when alloyed to CrB2-x and NbB2-x films. The formation of the a-BCx phase drastically improves the electrical contact resistance of the NbB2-x films. However, the mechanical properties are degraded, which result in a high friction and wear rate.

It was in TEM studies of the metastable amorphous structures for the Nb-Si-C films found that the electron beam induces crystallization. Hence, great care is required when studying these types of metastable structures.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 79 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1127
Keyword
thin film, coating, magnetron sputtering, nanocomposite, boride, carbide, electrical properties, mechanical properties
National Category
Materials Chemistry
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-219040 (URN)978-91-554-8886-4 (ISBN)
Public defence
2014-04-04, Polhemssalen, Ångströmslaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2014-03-13 Created: 2014-02-20 Last updated: 2014-04-29

Open Access in DiVA

No full text

Other links

Publisher's full text

Authority records BETA

Nedfors, NilsJansson, Ulf

Search in DiVA

By author/editor
Nedfors, NilsJansson, Ulf
By organisation
Inorganic Chemistry
In the same journal
Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films
Materials Chemistry

Search outside of DiVA

GoogleGoogle Scholar

doi
urn-nbn

Altmetric score

doi
urn-nbn
Total: 839 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf