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Phase Stability and Initial Oxidation of Ti2AlC Thin Films at 500 °C
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: 0000-0003-1785-0864
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.ORCID iD: 0000-0002-2837-3656
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Ti2AlC thin films deposited onto Al2O3 by magnetron sputtering have been annealed in vacuum and ambient air. The films consist of basal-plane-oriented grains with a fraction of nonbasal-plane-oriented grains with an out-of-plane orientation of [1013] and [1016] as shown by x-ray diffraction and scanning electron microscopy. The surface of the basalplane-oriented grains has (0001) terraces growth. In situ x-ray diffraction shows that the Ti2AlC phase decomposes during vacuum annealing at 700 °C, which is lower than what have been reported for bulk material. When oxidized in ambient air at 500 °C for 5 min oxide clusters of amorphous Al2O3 form in valleys between terraces. The oxides are formed by out-diffusion of Al along the basal planes and migration over the surface. X-ray photoelectron spectroscopy of a Ti2AlC film oxidized at 500 °C for 15 min shows oxides due to a parallel oxidation of Ti and Al.

National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-57521OAI: oai:DiVA.org:liu-57521DiVA: diva2:326283
Available from: 2010-06-22 Created: 2010-06-22 Last updated: 2016-08-31
In thesis
1. Thick and Thin Ti2AlC Coatings
Open this publication in new window or tab >>Thick and Thin Ti2AlC Coatings
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This Thesis explores the deposition techniques of magnetron sputtering and high velocity oxy-fuel (HVOF) spraying for Ti2AlC as a promising high-temperature material. Magnetron sputtering aims at producing thin (≤1 μm) Ti2AlC films of high crystal quality for use as a model system in understanding the material’s basic properties. HVOF is a new method for deposition of thick (≥200 μm) coatings by spraying Ti2AlC powder, with the aim of transferring the good bulk properties to coatings. The oxidation behavior of Ti2AlC coatings has been investigated for temperatures up to 1200 °C in air. As-deposited Ti2AlC(0001) thin films decompose into TiC during vacuum annealing at 700 °C by out-diffusion of Al as shown by x-ray diffraction analysis. The release of Al starts already at 500 °C in ambient air as driven by aluminum oxide formation on the film surface where the oxide initially forms clusters as observed by electron microscopy. While sputtering from a Ti2AlC target is simpler than by using different elemental targets, the resulting film composition differs from the target stoichiometry. This is due to differences in energy and angular distribution of the sputtered species and evaporation of Al at substrate temperatures above 700 °C. The composition can be compensated for by adding Ti to bind the Al and obtain phase-pure Ti2AlC coatings. For HVOF, I demonstrate how the total gas flow of a H2/O2 mixture (441-953 liter/min) and the powder grain size (30-56 μm) determine the thickness, density, and microstructure of the coatings. High gas flow and small grain size yield thick coatings of 210 μm with a low porosity of 2-8 % and a tensile stress of ≥80 MPa. A fraction of the Ti2AlC powder decomposes during spraying into TiC, Ti3AlC2, and Ti-Al alloys. The coatings also contain as much as 25 at.% O since the powder partly oxidizes during the spraying process. Increasing the powder size and decreasing the total gas flow yield a higher amount of Ti2AlC, but produces thinner coatings with lower cohesion. Post-annealing of the coatings at 900 °C in vacuum increases the Ti2AlC content due to a reversible phase transformation of the as-sprayed material. The high oxygen content, however, hinders the coating to completely transform into Ti2AlC and deteriorates its oxidation resistance. The work thus offers insights to the key parameters for optimizing Ti2AlC coating processing.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2010. 63 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1328
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-57525 (URN)978-91-7393-356-8 (ISBN)
Public defence
2010-09-03, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15
Opponent
Supervisors
Available from: 2010-06-22 Created: 2010-06-22 Last updated: 2016-08-31Bibliographically approved

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Frodelius, JennyEklund, PerHultman, Lars

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