How Al and Ta Diffusion Responses the Oxidation of NiCoCrAlYTa Coatings: Simulations

This paper is the second part of our series of studies on how Al and Ta diffusion responses the oxidation of NiCoCrAlYTa coatings by applying simulations. Thermodynamic and kinetic simulations were performed by using ThermoCalc and Dictra software. The NiCoCrAlYTa coatings with different Al and Ta addition at high temperatures showed typical gamma, gamma', beta phase microstructure which agreed with the thermodynamic calculations. The distribution of the elements in the developed microstructure during oxidation processes was also analyzed by simulation. An ¡°oxidation-diffusion¡± model was used to predict the microstructure evolution in the substrate coating system. The simulation successfully demonstrated that beta-NiAl phase was depleted as Al was oxidized and diffused into the substrate. gamma'-Ni3(Al,Ta) phase was formed as the ¦Â phase was depleted especially in a Ta rich MCrAlY coating. How Al and Ta diffusion interacts with the microstructure development in the materials was discussed in detail.