Modelling the microstructural evolution and degradation of M-Cr-Al-Y coatings during high temperature oxidation

A finite difference computer program has been developed to model the microstructural changes that occur in overlay coatings during simultaneous oxidation and interdiffusion with the base alloy. The degradation of the coating is predicted by modelling the aluminum concentrations in the coating and calculating the phase distribution from the Co-Cr-Al phase diagram. The results of the model are compared with experimental results for the isothermal oxidation of a Co-Cr-Al-Y coating on MM509 and a Co-24Cr alloy. Excellent agreement is found for cases where the diffusion coefficients are known.