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The Influence of Chemical and Phase Composition on Mechanical, Tribological and Electrical Properties of Silver-Aluminum alloys
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry. ABB AB, Corp Res, Insulat & Mat Technol, SE-72178 Vasterdas, Sweden.
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.
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2018 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 119, p. 680-687Article in journal (Refereed) Published
Abstract [en]

Ag1-xAlx alloys were investigated as potential sliding electrical contact materials. Seven Ag1-xAlx alloys, covering the different phase regions on the Ag-Al phase diagram, were prepared by arc melting. X-ray diffraction (XRD), scanning electron microscopy coupled with X-ray spectroscopy (SEM/EDX), X-ray photoelectron spectroscopy (XPS), nano- and microindentation, and four-point electrical contact resistance measurements were employed to characterize the composition, structure, and physicochemical properties of the alloys. The hardness of Ag1-xAlx alloys increases with Al content. The Ag1-xAlx alloys with hexagonal close-packed (hcp) structure exhibit better tribological properties than pure Ag and other phase compositions. The wear mechanisms change from adhesive, for the alloys with low Al content (<= 20 at. %) to oxidative and abrasive wear for the alloys with high Al content (>= 25 at. %). The Ag1-xAlx alloys with hcp structure exhibit the highest wear resistance. Depth-profile XPS data reveal that the oxide layer grows during the triboprocess and that its thickness increases with number of sliding cycles. Ag/Ag1-xAlx contact pairs exhibit higher contact resistance than the Ag/Ag pair and the contact resistance increases with Al content.

Place, publisher, year, edition, pages
2018. Vol. 119, p. 680-687
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:uu:diva-320229DOI: 10.1016/j.triboint.2017.11.026ISI: 000424960500066OAI: oai:DiVA.org:uu-320229DiVA, id: diva2:1088990
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy StorageAvailable from: 2017-04-18 Created: 2017-04-18 Last updated: 2018-04-04Bibliographically approved
In thesis
1. Synthesis, Characterization, and Evaluation of Ag-based Electrical Contact Materials
Open this publication in new window or tab >>Synthesis, Characterization, and Evaluation of Ag-based Electrical Contact Materials
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Ag is a widely used electrical contact material due to its excellent electrical properties. The problems with Ag are that it is soft and has poor tribological properties (high friction and wear in Ag/Ag sliding contacts). For smart grid applications, friction and wear became increasingly important issues to be improved, due to much higher sliding frequency in the harsh operation environment. The aim of this thesis is to explore several different concepts to improve the properties of Ag electrical contacts for smart grid applications.

Bulk Ag-X (X=Al, Sn In) alloys were synthesized by melting of metals. An important result was that the presence of a hcp phase in the alloys significantly reduced friction coefficients and wear rates compared to Ag. This was explained by a sliding-induced reorientation of easy-shearing planes in the hexagonal structure. The Ag-In system showed the best combination of properties for potential use in future contact applications. 

This thesis has also demonstrated the strength of a combinatorial approach as a high-throughput method to rapidly screen Ag-based alloy coatings. It was also used for a rapid identification of optimal deposition parameters for reactive sputtering of a complex AgFeO2 oxide with narrow synthesis window. A new and rapid process was developed to grow low frictional AgI coatings and a novel designed microstructure of nanoporous Ag filled with AgI (n-porous Ag/AgI) using a solution chemical method was also explored. The AgI coatings exhibited low friction coefficient and acceptable contact resistance. However, under very harsh conditions, their lifetime is too short. The initial tribotests showed high friction coefficient of the n-porous Ag/AgI coating, indicating an issue regarding its mechanical integrity.

The use of graphene as a solid lubricant in sliding electrical contacts was investigated as well. The results show that graphene is an excellent solid lubricant in Ag-based contacts. Furthermore, the lubricating effect was found to be dependent on chemical composition of the counter surface. As an alternative lubricant, graphene oxide is cheaper and easier to produce. Preliminary tests with graphene oxide showed a similar frictional behavior as graphene suggesting a potential use of this material as lubricant in Ag contacts.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. p. 98
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1517
Keywords
electrical contact, bulk, coating, Ag-based alloys, Ag-based delafossite, AgI, graphene, graphene oxide, combinatorial material science, dc magnetron sputtering, friction, wear, hardness, contact resistance
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-320235 (URN)978-91-554-9915-0 (ISBN)
Public defence
2017-06-08, Room 2001, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2017-05-18 Created: 2017-04-18 Last updated: 2017-06-07

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Taher, MamounMao, FangBerastegui, PedroJansson, Ulf

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