MCrAlX (M: Ni or Co no both, X: minor addition) coatings are widely used for oxidation and corrosion protection of superalloy components operating in the hot sections of advanced engines. Research work in this project has resulted in the development of two MCrAlX coatings with improved thermal cycling fatigue and oxidation resistance. Fe is added in one of the coatings, aiming at lowering the coating cost.
An oxidation-diffusion model, which can be used for selecting coating to match a particular substrate superalloy with regard to reducing chemical interactions between the coating and substrate, has also been established. In addition, with the help of literature survey and experiments, a new coating life criterion based on estimation of the Al-activity has been proposed and tested, which is more realistic than the conventional criterion based on microstructural changes.
The modeling work has assisted Siemens Industrial Turbomachinery in Finspång to select a proper coating and determined the coating thickness on a specific substrate superalloy for their turbine upgrading. Eventual use of the coatings in gas turbines after qualification is expected to contribute to better gas turbine performance and/or higher operating temperature of hot components. The application of the oxidation-diffusion model for coating selection as well as the use of Al-activity life criterion in design of hot components in gas turbines are also expected to lead to a more effective use of MCrAlX coatings for oxidation resistance due to the reduced substrate effect and more accurate estimation of coating life.
Results from further characterization of the coatings required for coating qualification as well as results from further test of the Al-activity life criterion will be obtained in the last year of project.
PhD student: Pimin Zhang
Participants: Dr Xin-Hai Li and Senior Prof. Sten Johansson
Project leader: Ru Lin Peng