Mechanical analysis and modeling of porous thermal barrier coatings

Abstract

Thermal barrier coatings (TBCs) are applied to the surface of components that are used in gas turbines and aircraft engines in order to increase the heat load. In this study, the cross-sectional microstructures of TBCs were investigated via scanning electron microscopy. After calculating the porosity and the pore size distribution, a two-dimensional finite element model with four different porosities (0, 1, 3, and 5%) were established. A stochastic method was used to generate a randomly distributed porous structure. Based on the results of FE analysis and nanoindentation tests, It was found that, at a high porosity (>3%), radial cracks are affected by the interaction between neighboring pores and occur at the top/bond coating interface. After the cooling stage, radial cracks continue their propagating trends. However, axial cracks are commonly generated from the ZrO2–8 wt.%Y2O3 surface as the tensile stress caused by a single micro-pore can be as much as three times higher than that of its surrounding area (porosity < 3%) at 1473 K. The addition of a 20 μm sealing layer can effectively eliminate the stress effects of the micro-pores on the YSZ coating surface.