title: Combinatorial Study of Gradient Ag-Al Thin Films: Microstructure, Phase Formation, Mechanical and Electrical Properties.
abstract: 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 Al-rich regions. No indication of a μ 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.
authors.affiliation: Department of Chemistry-Ångström Laboratory, Uppsala University , PO Box 538, SE-751 21 Uppsala, Sweden.
authors.forename: Fang
authors.initials: F
authors.lastname: Mao
authors.affiliation: Department of Chemistry-Ångström Laboratory, Uppsala University , PO Box 538, SE-751 21 Uppsala, Sweden.
authors.forename: Mamoun
authors.initials: M
authors.lastname: Taher
authors.affiliation: AGH University of Science and Technology , International Centre of Electron Microscopy for Materials Science and Faculty of Metals Engineering and Industrial Computer Science, Al. A. Mickiewicza 30, 30-059 Kraków, Poland.
authors.forename: Oleksandr
authors.initials: O
authors.lastname: Kryshtal
authors.affiliation: AGH University of Science and Technology , International Centre of Electron Microscopy for Materials Science and Faculty of Metals Engineering and Industrial Computer Science, Al. A. Mickiewicza 30, 30-059 Kraków, Poland.
authors.forename: Adam
authors.initials: A
authors.lastname: Kruk
authors.affiliation: AGH University of Science and Technology , International Centre of Electron Microscopy for Materials Science and Faculty of Metals Engineering and Industrial Computer Science, Al. A. Mickiewicza 30, 30-059 Kraków, Poland.
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Czyrska-Filemonowicz
authors.affiliation: Department of Chemistry-Ångström Laboratory, Uppsala University , PO Box 538, SE-751 21 Uppsala, Sweden.
authors.forename: Mikael
authors.initials: M
authors.lastname: Ottosson
authors.affiliation: ABB AB, Corporate Research , SE-721 78 Västerås, Sweden.
authors.forename: Anna M
authors.initials: AM
authors.lastname: Andersson
authors.affiliation: Department of Engineering Sciences, Uppsala University , PO Box 534, SE-751 21 Uppsala, Sweden.
authors.forename: Urban
authors.initials: U
authors.lastname: Wiklund
authors.affiliation: Department of Chemistry-Ångström Laboratory, Uppsala University , PO Box 538, SE-751 21 Uppsala, Sweden.
authors.forename: Ulf
authors.initials: U
authors.lastname: Jansson
keywords: Ag−Al alloy; adhesive wear; combinatorial approach; electrical contact; hexagonal phase; low friction