Microstructure Modifications to Enhance the Scattering Coefficient of Porous Yttria-Stabilized Zirconia Coatings.

In thermal barrier coatings (TBCs), the thermal radiative transfer becomes important in the overall heat transfer with higher turbine inlet temperature. The microstructure, including pore size distribution and pore morphology, primarily impacts TBCs' radiative properties. Modifying the microstructure is an effective method to change the radiative and overall heat transfer in TBCs. In this study, a new approach is developed to modify the microstructure of atmospheric plasma sprayed (APS) topcoats by mixing the fugitive polyester powder of various sizes into the base 8 wt.% yttria-stabilized zirconia (8YSZ) powder. By changing the polyester powder size and the volumetric mixing ratio, several 8YSZ films are fabricated, and their scattering coefficients are inverted from the directional-hemispherical transmittance and reflectance measurement in the infrared wavelength range. A detailed discussion of the microstructure changes due to the powder mixture and the resulting scattering coefficient changes is presented. The results show that mixing polyester with the 8YSZ powder is a very effective way to modify the microstructure of the topcoat and increase the scattering coefficient. A preferred microstructure that can result in a higher scattering coefficient will contain a higher fraction of interlamellar pores and large-size pores in the APS topcoat. [ABSTRACT FROM AUTHOR]