Investigation of boundary layers, oxidation resistance, and mechanical properties of halogenated γ-TiAl surfaces with ceramic thermal barrier coatings

Schu 729/22-1

Bild Forschungsprojekt

Hochtemperaturofen in Betrieb

Period: 2010-10-01 to 2013-09-30
Partners: DLR, TU Dresden
Funder: German Research Foundation (DFG)
Project Manager: Dr. Simone Friedle
Research Group: High Temperature Materials

Due to their excellent mechanical properties combined with a low density, intermetallic titanium aluminides are potential candidates to replace heavy Ni-based components in high-temperature applications, such as turbine blades in aero engines. The limited long-term oxidation resistance of γ-TiAl alloys at high temperatures is overcome by fluorine treatment to result in the formation of a thin, protective alumina scale on the surface, which enhances their corrosion stability at temperatures up to 1050°C. In order to further improve the oxidation resistance in γ-TiAl alloys, it is planned to additionally apply a ceramic thermal barrier coating (TBC) of yttria-stabilized zirconia to decrease the surface temperature. This method has already been applied for Ni-base superalloys. Here, the TBC cannot be directly applied onto the material and a bond coat of aluminum oxide has to be used in addition. In contrast, initial studies have shown that the dense alumina layer in pre-oxidized, fluorine-treated γ-TiAl alloys can serve as a bond coat and the TBC directly applied to the material.
In collaboration with our project partners from DLR Cologne and TU Dresden, the goal of our research project is to gain understanding of the complex relationship between oxidation and thermal protection of γ-TiAl alloys. Therefore, we will undertake microstructural and constitutional investigations of the boundary layers between the ceramic thermal barrier coating and the halogen-treated γ-TiAl, which contains a layer of aluminum oxide. Furthermore, the lifetime of the TBC and mechanical properties of the components, particularly under cyclic loading conditions, will be determined. In order to develop a practical application for these systems, they have to be optimized. The fluorine treatment of the samples, as well as pre-oxidation will be done at KWI. Deposition of the thermal barrier coatings will be done at the DLR Cologne via EB-PVD. Subsequent oxidation and corrosion experiments will be conducted at DFI and mechanical testing at TU Dresden.

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