A thermographic technique for the simultaneous estimation of in-plane and in-depth thermal diffusivities of TBCs

Absolute values and anisotropy of thermo-physical and mechanical properties of TBC are significantly affected by the microstructure. The thermal properties as a function of the specific microstructure along the different directions are therefore worth studying. In the present work a thermographic technique able to estimate in a single experiment both in-plane and in- depth thermal diffusivities of TBC has been described and the results obtained on three different freestanding APS TBC samples will be compared with the in-plane elastic modulus as measured by the three-point bending test. Depending on the microstructure and on the heat propagation direction, TBC thermal diffusivity in the range of 3-7×10-7 m2 s-1 has been found. The technique allows measuring the thermal diffusivity along two orthogonal directions highlighting, when present, any anisotropic in-plane structure. An analytical model has been applied to semi-quantitatively estimate both in-depth and in-plane thermal diffusivities of the three samples starting from quantitative image analysis characterization of sample micrographs obtained by scanning electron microscopy. The agreement between model and experimental data resulted quite satisfactory. The model accounts for the anisotropy of thermal diffusivity observed in some samples.