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Life time modelling of a thermal protection coating of gas turbine blades
Krukovski P.,
K.Tadlya(1), A.Rybnikov, I.Kryukov(2), V. Kolarik, M.Juez-Lorenzo(3)
An novel theoretical and experimental approach to life time modelling of MCrAlY coatings for stationary gas turbines has been undertaken using the Inverse Problem Solution (IPS) technique. With this technique feasible experimental data acquired after a defined experimental time ?e are used as input values for the model parameters estimation. In the first stage of the approach a model was assumed, which considers the Al concentration profile across the coating. The measured Al concentration profiles were used as input values for the model parameters estimation and a calculational prediction of the long-term diffusion and oxidation behaviour of the coating was performed.
Exposure experiments were carried out with an NiCoCrAlY coating containing 8 % Al in air at 950°C, currently up to 1000 h. Additionally, in situ studies of the oxide formation were performed in the first 100 hours by high temperature X-ray diffraction. The coating forms at 950°C a scale consisting of ?-Al2O3 and in the initial state smaller amounts of ?-Al2O3. The oxide scale is growing continuously and no other oxides were observed. The concentration profiles of Al across the coating thickness were determined by electron microprobe in the initial state and after 100, 300 and 1000 hours of oxidation. The concentration profile measured after 300 h was used as input values for the model parameters estimation in order to calculate the oxide scale thickness and the Al concentration profile after 1000 h.
The model describes already as a first simplified version with a high accuracy the experimentally determined aluminium depletion at the coating surface and at the coating - substrate interface as well as the oxide scale thickness after 100 and 300 h. The computational forecast for 1000 h at 950°C is in good agreement with the measured data. |