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Approximant Phases in Quasicrystalline AlCuFe Thin Films
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Quasicrystalline materials exhibit properties that are very different from conventional metallic materials. They are mostly metallic alloys, and show high hardness and stiffness but low electrical and thermal conductivity. The coefficient of friction and surface energy of the quasicrystalline materials are also very low. Approximants are a family of phases that are related to the quasicrystals. These phases share the local atomic arrangement of quasicrystals and have as a result many similar physical properties. Bulk quasicrystals are too brittle for many of the suggested applications, instead the most important area of applications concerns that of surface coatings.

In this work, quasicrystalline and approximant phases have been synthesized in thin films. Multilayered Al/Cu/Fe thin films, with a nominal global composition corresponding to the quasicrystalline phase, have been deposited by magnetron sputtering onto Si and Al2O3 substrates. During isothermal annealing at temperatures up to 700 °C homogeneous thin films were formed.

It is found that when using Si as substrate a film-substrate reaction occurs already below 390 °C, where Si diffuses into the film. This changes the composition, promoting the formation of the cubic α-approximant phase. Annealing at 600 °C for 4 h the cubic a-approximant phase forms in a polycrystalline state, with a small amount of a second phase, τ7-Al3Fe2Si3. The film is within 1.5 at.% of the ideal composition of the a-approximant phase, and contains 8 at.% Si. Continued annealing for 64 h provides for more diffusion of Si to 12 at.%, which result in an increase of the t7-phase. The rate of Si in-diffusion was observed to decrease with annealing time, and the lattice parameter of the a-phase was continuously decreasing as diffused Si substituted for Al. No degradation of the crystal quality of the remaining α-phase was observed even after as much as 150 h of treatment.

When annealing the same Al/Cu/Fe thin film grown on non-reactant Al2O3 substrates the icosahedral Al62.5Cu25Fe12.5 quasicrystalline phase is formed.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. , 43 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1536
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-77384Local ID: LIU-TEK-LIC-2012:21ISBN: 978-91-7519-871-2 (print)OAI: oai:DiVA.org:liu-77384DiVA: diva2:526602
Presentation
2012-05-10, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2012-05-14 Created: 2012-05-14 Last updated: 2016-08-31Bibliographically approved
List of papers
1. Formation of α-approximant and quasicrystalline Al-Cu-Fe thin films
Open this publication in new window or tab >>Formation of α-approximant and quasicrystalline Al-Cu-Fe thin films
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Multilayered Al-Cu-Fe thin films have been deposited by magnetron sputtering onto Si and Al2O3 substrates with a nominal global composition corresponding to the quasicrystalline phase, 5:2:1. Subsequent annealing was performed on samples up to 710 °C. It is found that when using Si as substrate a film-substrate reaction occurs already below 390 °C, where Si diffuses into the film. This changes the composition, promoting the formation of the α-approximant Al55Si7Cu25.5Fe12.5 in the temperature range 400 to 650 °C over the quasicrystalline ψ-phase. When annealing the same Al-Cu-Fe thin film grown on Al2O3 substrates the Al62.5Cu25Fe12.5 icosahedral quasicrystalline phase is formed.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-77382 (URN)
Available from: 2012-05-14 Created: 2012-05-14 Last updated: 2016-08-31Bibliographically approved
2. Structure and Composition of Approximant Thin Films Formed by Substrate Diffusion
Open this publication in new window or tab >>Structure and Composition of Approximant Thin Films Formed by Substrate Diffusion
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Multilayered Al/Cu/Fe thin films with composition close to the quasicrystalline phase have been prepared by magnetron sputtering. Annealing at 600 °C yields a homogeneous film of the cubic approximant phase by Si substrate diffusion, which prevented the formation of the quasicrystalline phase. After 4 h annealing the film contained 8 at.% Si corresponding well to the expected value of the approximant. The amount of Si in the films is found to slowly increase to ~12 at.% during continued annealing (64 h) while the approximant phase was retained. The lattice parameter was continuously decreasing as Si substituted for Al.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-77383 (URN)
Available from: 2012-05-14 Created: 2012-05-14 Last updated: 2016-08-31Bibliographically approved

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Olsson, Simon

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