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Improvement of the High-Temperature Oxidation Resistance of γ-TiAl by Selectively Pre-treated Si-based Coatings

Ebach-Stahl, Andrea and Fröhlich, Maik and Braun, Reinhold and Leyens, Christoph (2008) Improvement of the High-Temperature Oxidation Resistance of γ-TiAl by Selectively Pre-treated Si-based Coatings. Advanced Engineering Materials, 10 (7), pp. 675-677. Wiley-VCH Verlag GmbH. doi: 10.1002/adem.200800061.

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In this study the degradation of the oxidation resistance of γ-TiAl alloys caused by the high affinity of titanium for oxygen was mitigated by forming thermodynamically stable titanium silicides on the surface. A Si-25at%Ti-coating was deposited on Ti-45Al-8Nb (at%) substrate by means of magnetron sputtering. To form surface layers of thermodynamically stable titanium silicides an optimized pre-treatment process at 1000°C for 100h at 10<sup>-6</sup>mbar was used applying slow heating and cooling rates. This annealing process resulted in the formation of a Ti<sub>5</sub>Si<sub>3</sub> phase and a Ti<sub>5</sub>Si<sub>4</sub> layer on top, whereas titanium silicides with higher silicon content (Ti<sub>5</sub>Si<sub>4</sub>, TiSi and TiSi<sub>2</sub>) formed when the coating system was pre-treated in air at 750°C for 100h. During latter pre-treatment, a mixed oxide scale grew on top of the coating. The oxidation behavior of the pre-treated coatings on γ-TiAl was studied by cyclic testing at 900°C in air. Phase formation and microstructure evolution of the coated samples were investigated after 10, 100 and 1000 cycles using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis. All specimens exhibited a mixed oxide scale on top after cyclic testing and exceeded a lifetime of 1000 cycles at minimum. Uncoated γ-TiAl failed after 520 cycles at 900°C by severe scale spallation.

Item URL in elib:https://elib.dlr.de/56462/
Document Type:Article
Title:Improvement of the High-Temperature Oxidation Resistance of γ-TiAl by Selectively Pre-treated Si-based Coatings
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Date:1 July 2008
Journal or Publication Title:Advanced Engineering Materials
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In ISI Web of Science:No
DOI :10.1002/adem.200800061
Page Range:pp. 675-677
Publisher:Wiley-VCH Verlag GmbH
Keywords:oxidation protective coatings, titanium aluminides, titanium silicides, cyclic oxidation
HGF - Research field:Aeronautics, Space and Transport (old)
HGF - Program:Aeronautics
HGF - Program Themes:Propulsion Systems (old)
DLR - Research area:Aeronautics
DLR - Program:L ER - Engine Research
DLR - Research theme (Project):L - Turbine Technologies (old)
Location: Köln-Porz
Institutes and Institutions:Institute of Materials Research > High Temperature and Functional Coatings
Deposited By: Ebach-Stahl, Andrea
Deposited On:03 Dec 2008
Last Modified:27 Apr 2009 15:32

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