Modeling Thermally Grown Oxides In Thermal Barrier Coatings Using Koch Fractal

Growth of the Thermally Grown Oxide (TGO) between the bond coat and thermal barrier coating (TBC) during service is one of the most common causes of failure within thermal barrier coating (TBC) systems. Initially this oxide will provide protection from oxidation for the substrate, but stress build up will contribute to delamination of the topcoat. Research has been carried out over the stresses caused by this TGO growth, and how to best mitigate these induced stresses. The interface topography plays a critical role for air plasma sprayed (APS) TBCs in development of stress profiles across the TGO/TBC interface [1, 2]. The APS TBCs fail by cracking in the TBC close to the TGO-TBC interface. Most models treat TGO as a sinusoidal wavelength interface. However, most TGO surfaces have been experimentally observed to have fractal like patterns at the interfacial region of the bondcoat and topcoat. Fractals provide us a better understanding of interactions at rough interfaces between two materials adhered to one another. In this work, we model the topography of the TGO using a Koch fractal. We find the geometry selected to model the TGO layer has a direct effect on the stress generation and creep strain during simulation.