Thermally Sprayed Oxidation Protection Coatings for γ-TiAl Substrates

Abstract Due to excellent mechanical properties and low density compared to super alloys (e.g. Ni-based alloys) Titanium Aluminide is often used as base material in the aerospace industry. But the thermodynamic conditions within turbines limit the capabilities of the material. At the moment γ-TiAl is used for parts, which have to withstand temperatures up to 700 °C. Above this temperature oxidation kinetics cause a thick oxide layer consisting of several oxides, which tend to fast chipping. Therefore the surface of the γ-TiAl is being destroyed and the material loses its excellent mechanical properties. To enable the use of this material at higher temperatures, the development of an oxidation protection coating is necessary. Several coating techniques e.g. EB-PVD were tried in the last years, but the oxidation behaviour of the γ-TiAl could not be significantly improved. Protective thermal spray coatings so far seem to be a promising technology in order to protect γ-TiAl components against oxidation. Therefore this technique was used within this work, which aims for the development of new oxidation protection coatings. A multilayer system was developed. The multilayer consists of a ceramic ZrO2-7Y2O3 coating with a NiCoCrAlY top coat. In this case the ceramic coating avoids the diffusion of Ti or Al of the γ-TiAl into the MCrAlY coating or the other way around. The NiCoCrAlY coating improved the oxidation behaviour of the Titanium Aluminide by building a dense oxide layer on top of the multilayer. The paper will give an overview about the results of the oxidation tests with the new developed multilayer concept for protection of the γ-TiAl against oxidation.