A Comparative Experimental Study on Radiative Properties of EB-PVD and Air Plasma Sprayed Thermal Barrier Coatings

Abstract

In this paper, the radiative properties of electron beam physical vapor deposition (EB-PVD) and air plasma sprayed (APS) partially yttria stabilized zirconia (YSZ) thermal barrier coatings (TBCs) have been comparatively studied for the first time by measuring the spectral diffuse reflectance and transmittance in a broad spectral band ranging from 250 nm to 15 μm. The radiation transfer mechanisms inside the coatings are explored based on the experimental data and theoretical model. The results indicate that the distinctive micronanostructures of APS and EB-PVD coatings have an important effect on the radiative heat transfer. In particular, the larger grain boundary and the total porosity strongly affect the volume scattering properties of the coatings, and the scattering coefficient is closely related to the arrangement of grain boundary as well as the pore architecture (i.e., its size, morphology, and its distribution). Compared to the laminar microstructure of APS TBCs, the columnar microstructure of EB-PVD freestanding coatings exhibits a higher transmittance, a lower reflectance, and a larger absorption in the spectral region from 400 nm to 10 μm, which leads to an increase of the total heat flux. By modifying the microstructure of TBCs properly, the radiative heat flux can be reduced and thereby providing a better thermal protection for the metallic substrate.