Oxidation of MCrAlY coatings on Ni based superalloys

Industrial gas turbine engines used for power generation generally employ Ni based superalloys for the turbine blades. The operating conditions for these blades are very arduous with high temperatures (>900°C) leading to oxidation and corrosion. Therefore in order to increase the service life of components, coatings are employed which allow the use of Ni based superalloys at higher temperatures and therefore more efficient engines. These systems are very complicated and in order to understand coating performance and service life, many modelling approaches have been utilised. However, there is still a lack of understanding of the thermally grown oxide (TGO) with regards to its chemistry, microstructure, adhesion strength and mechanical properties. Therefore a more detailed understanding of the TGO would be useful for both empirical and computational modelling. The effect of compositional changes in the MCrAlY bond coat and their effect on the TGO have been studied. Two different MCrAlY coatings have been examined after aging at representative operation temperatures. A number of analytical techniques have been used including, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray and electron backscattered diffraction. A dual beam scanning electron microscope has also been utilised for both TEM sample preparation and microstructural evaluation. These techniques will allow a better understanding of the microstructure of the TGO, ultimately leading to improved predictions of coating behaviour and service life.