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Thick and Thin Ti2AlC Coatings
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
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: urn:nbn:se:liu:diva-57525ISBN: 978-91-7393-356-8 (print)OAI: oai:DiVA.org:liu-57525DiVA: diva2:326314
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
List of papers
1. Ti2AlC coatings deposited by High Velocity Oxy-Fuel spraying
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2008 (English)In: Surface and Coatings Technology, ISSN 0257-8972, Vol. 202, no 24, 5976-5981 p.Article in journal (Refereed) Published
Abstract [en]

High Velocity Oxy-Fuel has been utilized to spray coatings from Ti2AlC (MAXTHAL 211®) powders. X-ray diffraction showed that the coatings consist predominantly of Ti2AlC with inclusions of the phases Ti3AlC2, TiC, and Al–Ti alloys. The fraction of Ti2AlC in coatings sprayed with a powder size of 38 μm was found to increase with decreasing power of the spraying flame as controlled by the total gas flow of H2 and O2. A more coarse powder (56 μm) is less sensitive to the total gas flow and retains higher volume fraction of MAX-phase in the coatings, however, at the expense of increasing porosity. X-ray pole figure measurements showed a preferred crystal orientation in the coatings with the Ti2AlC (000l) planes aligned to the substrate surface. Bending tests show a good adhesion to stainless steel substrates and indentation yields a hardness of 3–5 GPa for the coatings sprayed with a powder size of 38 μm.

Place, publisher, year, edition, pages
Elsevier, 2008
Keyword
MAX-phase, High Velocity Oxy-Fuel (HVOF), Phase transitions, X-ray diffraction, Scanning electron microscopy (SEM)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-13102 (URN)10.1016/j.surfcoat.2008.06.184 (DOI)
Available from: 2008-04-01 Created: 2008-04-01 Last updated: 2016-08-31
2. Microstructure of high velocity oxy-fuel sprayed Ti2AlC coatings
Open this publication in new window or tab >>Microstructure of high velocity oxy-fuel sprayed Ti2AlC coatings
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2010 (English)In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 45, no 10, 2760-2769 p.Article in journal (Refereed) Published
Abstract [en]

The microstructure formation and phase transformations in Ti2AlC-rich coatings deposited by High Velocity Oxy-fuel spraying of Maxthal 211(A (R)) powders is presented. High resolution electron microscopy analysis, using both scanning and transmission electron microscopy with energy dispersive spectrometry and energy filtering, combined with X-ray diffraction reveals that the coatings consist of Ti2AlC grains surrounded by regions of very small TiC grains embedded in Ti (x) Al (y) . The composition of the Ti (x) Al (y) depends on its surrounding and varies with size and distribution of the adjacent TiC grains. Impact of spray parameters on coating microstructure is also discussed. Two spray parameters were varied; powder size distribution and flame power. They were found to greatly affect the coating microstructure. Increasing powder size and decreasing flame power increase the amount of Ti2AlC, but produces thinner coatings with lower cohesion. Larger powder size will also decrease oxygen incorporation.

Place, publisher, year, edition, pages
Springer, 2010
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-54608 (URN)10.1007/s10853-010-4263-4 (DOI)000275457100029 ()
Available from: 2010-03-26 Created: 2010-03-26 Last updated: 2017-12-12
3. Annealing of thermally sprayed Ti2AlC coatings
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2011 (English)In: INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, ISSN 1546-542X, Vol. 8, no 1, 74-84 p.Article in journal (Refereed) Published
Abstract [en]

Phase transformations during annealing of coatings sprayed with the High Velocity Oxy-Fuel technique using Ti2AlC powder have been investigated by in-situ x-ray diffraction. The asdeposited coatings, consisting of Ti2AlC, Ti3AlC2, TiC, Ti-Al, and oxides, are stable up to 500 °C. Ti3AlC2 forms above 550 °C and Ti2AlC forms above 700 °C by intercalation of Al into TiCx. For temperatures between 900 and 1100 °C, Ti3AlC2 and Ti2AlC decompose by losing Al to the surrounding matrix resulting in TiCx, and Al2O3. The thermal expansion coefficient between ambient and 700°C is 11.9·10-6 K-1. The thermal diffusivity at room temperature is 1.9·10-6 m2/s.

Place, publisher, year, edition, pages
Blackwell, 2011
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-57516 (URN)10.1111/j.1744-7402.2010.02569.x (DOI)000285968600009 ()
Available from: 2010-06-22 Created: 2010-06-22 Last updated: 2016-08-31
4. Oxidation of Ti2AlC bulk and spray deposited coatings
Open this publication in new window or tab >>Oxidation of Ti2AlC bulk and spray deposited coatings
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2010 (English)In: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 52, no 12, 3955-3961 p.Article in journal (Refereed) Published
Abstract [en]

The oxidation behaviour of Ti2AlC bulk and high velocity oxy-fuel spray deposited coatings has been investigated for temperatures up to 1200 °C. X-ray diffraction and electron microscopy show that bulk Ti2AlC forms a continuous layer of a-Al2O3 below a layer of TiO2 at temperatures as low as 700 °C. Oxidation of the Ti2AlC coatings is more complex, and also involves the phases Ti3AlC2, TiC, and TixAly, formed during the spraying process. a-Al2O3 is observed, however, it is unevenly distributed deep into the material, and does not form a continuous layer essential for good oxidation resistance.

Place, publisher, year, edition, pages
Elsevier, 2010
Keyword
Aluminium, Ceramic, Titanium, SEM, XRD, Oxidation
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-57520 (URN)10.1016/j.corsci.2010.08.004 (DOI)000283961400015 ()
Available from: 2010-06-22 Created: 2010-06-22 Last updated: 2017-12-12
5. Sputter deposition from a Ti2AlC target: Process characterization and conditions for growth of Ti2AlC
Open this publication in new window or tab >>Sputter deposition from a Ti2AlC target: Process characterization and conditions for growth of Ti2AlC
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2010 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 518, no 6, 1621-1626 p.Article in journal (Refereed) Published
Abstract [en]

Sputter deposition from a Ti2AlC target was found to yield Ti-Al-C films with a composition that deviates from the target composition of 2:1:1. For increasing substrate temperature from ambient to 1000 degrees C, the Al content decreased from 22 at.% to 5 at.%, due to re-evaporation. The C content in as-deposited films was equal to or higher than the Ti content. Mass spectrometry of the plasma revealed that the Ti and Al species were essentially thermalized, while a large fraction of C with energies andgt;4 eV was detected. Co-sputtering with Ti yielded a film stoichiometry of 2:0.8:0.9 for Ti:Al:C, which enabled growth of Ti2AlC. These results indicate that an additional Ti flux balances the excess C and therefore provides for more stoichiometric Ti2AlC synthesis conditions.

Place, publisher, year, edition, pages
Elsevier, 2010
Keyword
MAX phase, Titanium carbide, Compound target, Physical vapor deposition, X-ray diffraction
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-54250 (URN)10.1016/j.tsf.2009.11.059 (DOI)000274812200001 ()
Note
Original Publication: Jenny Frodelius, Per Eklund, Manfred Beckers, Per Persson, Hans Högberg and Lars Hultman, Sputter deposition from a Ti2AlC target: Process characterization and conditions for growth of Ti2AlC, 2010, THIN SOLID FILMS, (518), 6, 1621-1626. http://dx.doi.org/10.1016/j.tsf.2009.11.059 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/ Available from: 2010-03-05 Created: 2010-03-05 Last updated: 2017-12-12
6. Phase Stability and Initial Oxidation of Ti2AlC Thin Films at 500 °C
Open this publication in new window or tab >>Phase Stability and Initial Oxidation of Ti2AlC Thin Films at 500 °C
(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:nbn:se:liu:diva-57521 (URN)
Available from: 2010-06-22 Created: 2010-06-22 Last updated: 2016-08-31

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