Modeling the thermal radiation properties of thermal barrier coatings based on a random generation algorithm

Abstract

Thermal barrier coatings (TBCs) are porous media in which many different pores and cracks are induced by different manufacturing procedures. Many studies have been conducted to investigate the impact of microstructures of TBCs on thermal conductivity; nevertheless, the influence of microstructures on the radiative properties of TBCs has not drawn significant attention. In addition, the working condition of thermal barrier coatings is at high temperatures at which the contribution of radiative heat transfer plays a very crucial role. Therefore, it is necessary to study the radiative properties of TBCs to characterize their insulation performance. In this work, the microstructures of air-plasma- sprayed (APS) 8wt% yttria stabilized zirconia (8YSZ) thermal barrier coatings (TBCs) are constructed by the quartet structure generation set (QSGS) algorithm. A finite-difference-time-domain (FDTD) method is carried out to simulate radiative heat transfer through TBCs. Three parameters—average pore size, directional growth probability Di (especially horizontal growth probability D13) and porosity—have been investigated to study the microstructural effect on the radiative properties of TBCs. The reflectance of freestanding 50-μm-thick thermal barrier coatings is studied using Lumerical FDTD Solutions in the wavelength range from 1 to 6μm at normal incidence. The absorption and scattering coefficient as a function of wavelength are extracted using the four-flux model. The results will help us to characterize the radiative heat transfer process across the TBCs and provide us with a theoretical guide to design TBCs with a high thermal insulation property.