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Combinatorial Study of Gradient Ag-Al Thin Films: Microstructure, Phase Formation, Mechanical and Electrical Properties
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.
AGH Univ Sci & Technol, Int Ctr Electron Microscopy Mat Sci, Al A Mickiewicza 30, PL-30059 Krakow, Poland.;AGH Univ Sci & Technol, Fac Met Engn & Ind Comp Sci, Al A Mickiewicza 30, PL-30059 Krakow, Poland..
AGH Univ Sci & Technol, Int Ctr Electron Microscopy Mat Sci, Al A Mickiewicza 30, PL-30059 Krakow, Poland.;AGH Univ Sci & Technol, Fac Met Engn & Ind Comp Sci, Al A Mickiewicza 30, PL-30059 Krakow, Poland..
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2016 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 8, no 44, p. 30635-30643Article in journal (Refereed) Published
Abstract [en]

A combinatorial approach is applied to rapidly deposit and screen Ag-Al thin films-to evaluate the mechanical, tribological, and electrical properties as a function of chemical composition. Ag-Al thin films with large continuous composition gradients (6-60 atom % Al) were deposited by a custom-designed combinatorial magnetron sputtering system. X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), scanning and transmission electron microscopy (SEM and TEM), X-ray photoelectron spectroscopy (XPS), nanoindentation, and four-point electrical resistance screening were employed to characterize the chemical composition, structure, and physical properties of the films in a time-efficient way. For low Al contents (<13 atom %), a highly (111)-textured fcc phase was formed. At higher Al contents, a (002)-textured hcp solid solution phase was formed followed by a fcc phase in the most At-rich regions. No indication of a mu phase was observed. The Ag-Al films with fcc-Ag matrix is prone to adhesive material transfer leading to a high friction coefficient (>1) and adhesive wear, similar to the behavior of pure Ag. In contrast, the hexagonal solid solution phase (from ca. 15 atom %Al) exhibited dramatically reduced friction coefficients (about 15% of that of the fcc phase) and dramatically reduced adhesive wear when tested against the pure Ag counter surface. The increase in contact resistance of the Ag Al films is limited to only 50% higher than a pure Ag reference sample at the low friction and low wear region (19-27 atom %). This suggests that a hcp Ag Al alloy can have a potential use in sliding electrical contact applications and in the future will replace pure Ag in specific electromechanical applications.

Place, publisher, year, edition, pages
2016. Vol. 8, no 44, p. 30635-30643
Keyword [en]
Ag-Al alloy, combinatorial approach, low friction, adhesive wear, hexagonal phase, electrical contact
National Category
Materials Chemistry Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-310756DOI: 10.1021/acsami.6b10659ISI: 000387737200089OAI: oai:DiVA.org:uu-310756DiVA, id: diva2:1058036
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage, 38432-1Knut and Alice Wallenberg FoundationSwedish Foundation for Strategic Research
Available from: 2016-12-20 Created: 2016-12-19 Last updated: 2017-11-29Bibliographically 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
Keyword
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)
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Supervisors
Available from: 2017-05-18 Created: 2017-04-18 Last updated: 2017-06-07

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