Lifetime prediction for MCrAlY coatings by means of inverse problem solution (IPS)

The method of inverse problem solution (IPS) has been applied to modeling and lifetime prediction of MCrAlY coatings for stationary gas turbine applications. With this technique feasible experimental data like β-NiAl–phase and/or Al concentration profiles acquired after a defined time τe are used as input values for the model parameter estimation. The lifetime prediction procedure then calculates the β-NiAl–phase depletion until the complete consumption, which is defined as lifetime end of the coating. The lifetime prediction approach has been performed on a NiCoCrAlY coating with 8% Al in air at 900 and 950 °C and verified by experiments up to 10 000 h. Additionally, in situ studies of the oxide scale formation in the first 100 h were carried out. The coating forms at both temperatures α-Al2O3 and initially θ-Al2O3, which influences the initial kinetics and transforms on further oxidation into α-Al2O3. The β-NiAl–phase and the Al concentration profiles were determined in the initial state, after 700 and 10 000 h of oxidation. The profiles measured after 700 h were used as input values for the model parameter estimation and those after 10 000 for verification. With these values, the β-NiAl depletion and the oxide scale thickness were calculated as a function of time yielding the lifetime prediction of the coating. The procedure delivers highly reliable lifetime prediction and allows to evaluate the influence of the coating thickness on the lifetime.