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Tuning tribological, mechanical and electrical properties of Ag-X (X=Al, In, Sn) alloys
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, Inorganic Chemistry.
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2018 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 125, p. 121-127Article in journal (Refereed) Published
Abstract [en]

A new design concept for silver based alloys with a hexagonal structure as electrical contact materials with enhanced tribological properties has been investigated. The correlations between the phase composition and the tribological properties have been investigated in the Ag-Al, Ag-In and Ag-Sn systems. In each system, alloys with different chemical compositions were prepared by melting in evacuated ampoules. Characterisation techniques such as: optical microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning and transmission electron microscopies (SEM and TEM) have been used to evaluate the microhardneas, tribological properties and contact resistance of the samples. The phase compositions of the synthesized Ag-Al and Ag-Sn alloys were in agreement with the phase diagrams and the metastable hcp phase was observed in the Ag-In system. The friction coefficients and wear rates of all the hcp-Ag-X (X = Al, In, Sn) alloys were considerably lower than pure Ag or fcc-Ag alloys. This is attributed mainly to easily shearing basal planes in the hcp structure. The Ag-Sn alloys showed high contact resistances, making them less suitable for a sliding electrical contacts. In contrast, the Ag-In alloys showed much lower contact resistance, making them better alternatives for practical applications.

Place, publisher, year, edition, pages
2018. Vol. 125, p. 121-127
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:uu:diva-320227DOI: 10.1016/j.triboint.2018.04.020ISI: 000435747800014OAI: oai:DiVA.org:uu-320227DiVA, id: diva2:1088983
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage, 38432-1Available from: 2017-04-18 Created: 2017-04-18 Last updated: 2018-08-27Bibliographically 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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