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The role of diffusion and oxidation kinetics in a coating life prediction code – application to components

pubblicazioni - Articolo

The role of diffusion and oxidation kinetics in a coating life prediction code – application to components

code – application to components Claudia Rinaldi*, Marco Mandelli** ASME TURBO EXPO 2009, Orlando, USA, 8-12 Giugno 2009 * CESI RICERCA ** PROING ITALIA Under the umbrella of an Italian R&D programme, furnace-cyclic tests of thermal barrier coating (TBC) specimens were carried out to study the coating/substrate interactions and to determine a quantitative description of the degradation as induced by diffusion and oxidation at the interface of TBC and the bond coat (BC). On the basis of these experiments a coating life prediction code was developed, which utilized two alternative approaches for the oxidation kinetics of BC: “phenomenological” oxidation law and “free kinetics” oxidation behaviour. In this paper, the capability is shown of the latter methodology to predict more reliably the oxide thickness, the formation of non alumina oxide and formation of Kirkendall voids. The model was tested for MCrAlY and MCrAlYRe bond coats deposited by different thermal spray processes on various alloys. Examples of predictions are shown together with some comparisons with the experimental findings on the exposed specimens or ex-service components. Finally the oxidation kinetics is discussed with regards to the influence of the presence of TBC on the oxidation process in BC, taking into consideration that alumina and Zirconia – Yttria properties and their interactions. The inverse problem solution (IPS) method was applied together with the developed code to estimate the local mean operating temperature on the component surface. Some examples of code application to ex- service components are also shown.

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