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Formation of α-approximant and quasicrystalline Al-Cu-Fe thin films
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.ORCID iD: 0000-0002-2837-3656
2012 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 526, 74-80 p.Article in journal (Refereed) Published
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 the samples up to 710 degrees C. It is found that when using Si as a substrate a film-substrate reaction occurs already below 390 degrees C, where Si diffuses into the film. This changes the composition, promoting the formation of the alpha-approximant Al55Si7Cu25.5Fe12.5 in the temperature range 400 to 650 degrees C over the quasicrystalline psi-phase. When annealing the same Al-Cu-Fe thin film grown on Al2O3 substrates the Al62.5Cu25Fe12.5 icosahedral quasicrystalline phase is formed.

Place, publisher, year, edition, pages
Elsevier , 2012. Vol. 526, 74-80 p.
Keyword [en]
Quasicrystal, Approximant, Al-Cu-Fe-Si, X-ray diffraction, Annealing, Phase evolution, Multilayer, Sputtering
National Category
Engineering and Technology
URN: urn:nbn:se:liu:diva-89532DOI: 10.1016/j.tsf.2012.11.009ISI: 000313703200012OAI: diva2:608213

Funding Agencies|Swedish Foundation for Strategic Research (SSF) Strategic Research Center in Materials Science for Nanoscale Surface Engineering (MS2E)||

Available from: 2013-02-26 Created: 2013-02-26 Last updated: 2016-08-31
In thesis
1. Al-based Thin Film Quasicrystals and Approximants
Open this publication in new window or tab >>Al-based Thin Film Quasicrystals and Approximants
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this work, Al-based quasicrystalline and approximant phases have been synthesized in thin films using magnetron sputter deposition. Quasicrystals are structures having long-range order and rotational symmetries which are inconsistent with periodicity. Due to their unusual structure, quasicrystals show many anomalous and unique physical properties, including; high hardness, wear resistance, low friction, and low electrical and thermal conductivities. Approximants are a family of periodic 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, and instead the most important area of applications concerns that of surface  coatings.

Multilayered Al/Cu/Fe thin films, with a nominal global composition   corresponding to the quasicrystalline phase, have been deposited onto Si and Al2O3 substrates. During isothermal annealing at temperatures up to 700 °C homogeneous thin films were formed. When Si was used as substrate a film-substrate reaction occured already below 390 °C, where Si diffused into the film. This changed the composition, and promoted the formation of the cubic α-approximant phase. Annealing at 600 °C for 4 h the cubic α-approximant phase formed in a polycrystalline state, with a small amount of a second phase, τ7-Al3Fe2Si3. The film was within 1.5 at.% of the ideal composition of the α-approximant phase and contained 8 at.% Si. Continued annealing for 64 h provided for more diffusion of Si to 12 at.%. No degradation of the crystal quality of the remaining α-phase was observed even after as much as 150 h of treatment.

Nanomechanical and nanotribological properties, including hardness, elastic modulus, friction and toughness, were investigated for the approximant and quasicrystalline samples. The approximant phase, annealed at 600 °C for 4 h, proved to be harder and had higher elastic modulus values than the quasicrystalline phase, about, 15.6 GPa and 258 GPa, respectively. The fracture toughness of the approximant, on the other hand, <0.1 MPa/m½, was inferior to that of the quasicrystals with 1.5 MPa/m½. Low friction coefficients of about 0.13 were measured for both phases.

When annealing multilayered Al/Cu/Co thin films on Al2O3 the decagonal quasicrystal d-Al-Cu-Co was formed at 500 °C. The XRD peak intensities were rather low, but after raising the temperature to 850 °C a large increase in intensity and a complete texturing with the 10-fold periodic axis aligned with the substrate normal occurred. When annealing the same samples on Si, the decagonal quasicrystal was again found, however, TEM and EDX measurements identified 3-6 at.% Si inside the quasicrystalline grains. Also the decagonal d-Al-Cu-Co-Si quasicrystal was textured with the 10-fold periodic axis aligned with the surface normal. The texture was however not complete as in the thin films grown on Al2O3. Raising the temperature to over 700 °C led to the formation of other crystalline phases in favor of the decagonal d-Al-Cu-Co-Si.

For the Cu-Al-Sc system quasicrystalline thin films were grown directly from the vapor phase by utilizing ion-assistance during growth at low temperatures, thus eliminating the need for post-annealing. Diffraction experiments revealed that amorphous films were formed at room temperature. The quasicrystalline phase formed at a substrate temperature of 340 °C with an improved quality at higher temperatures up to 460 °C. The quasicrystal film quality was improved by increasing the ion-flux during with ion energies of 26.7 eV. Increasing the ion energy further was however found to cause resputtering and defects in the films. Electron microscopy revealed a polycrystalline microstructure with crystal grains in the shape of thin needles.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. 61 p.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1538
National Category
Natural Sciences
urn:nbn:se:liu:diva-96910 (URN)978-91-7519-537-7 (ISBN)
Public defence
2013-09-27, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Available from: 2013-08-29 Created: 2013-08-29 Last updated: 2016-08-31Bibliographically approved

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