Development of novel creep resistant bond coats for “Environmental Barrier Coatings”

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SiC-fiber reinforced SiC-composites as high temperature materials exhibit high potential for applications in aircraft engines as well as stationary gas turbines. The SiC-composites can realize higher inlet temperatures compared with Ni-based superalloys. Under application conditions both in aircraft engines and in stationary gas turbines the components of SiC-composites must be protected against water vapor induced losses using an environmental barrier coating (EBC) system. The life time of modern EBC systems depends among others on the properties of the Si bond coat. A high creep resistance of the Si bond coat is very important for the whole EBC system. The purpose of this project is the development of novel Si-based bond coats for modern EBC systems with enhanced creep resistance. In this way, the life time of the EBC system will be increased. Within the scope of this project, new developments with respect to materials and process technology will be carried out to achieve the aim. Die novel coating materials will be based on Si/Si3N4- and Si/SiC-composites. These composites can increase the creep resistance of the Si-based bond coats due to Si3N4- and SiC-reinforcing. The increased creep resistance will enhance the life time of the thermally grown oxide (TGO) scale on the bond coat and thus of the whole EBC system. The corresponding spray powders will be designed and developed. The bond coats will be produced by plasma spraying as well as by HVOF spraying. Die spray parameters will be developed for both spray processes to produce dense and homogenous microstructures. In addition to a characterization of the microstructures and phase compositions and investigation of the mechanical and thermo-physical properties, the novel bond coats will be investigated with regard to TGO-formation, -growth and damage mechanisms by isothermal exposition and by thermal cyclic tests at high temperatures of such as T=1,300 °C. Finally, the possibility of further improvement of the coating properties by heat-treatment will be studied as well.