Abstract
Microstructure has a significant influence on the thermal conductivity of thermal barrier coating (TBC) systems. In this work, the microstructures including splat interface, monoclinic phase and grain boundaries in the YSZ air plasma spraying (APS) TBC systems are investigated. A finite element simulation model based on electron backscatter diffraction (EBSD) images is established. It is found that the simulation results of thermal conductivity are in good agreement with the experimental results. Using this model, the effect coefficient of splat interface, monoclinic phase and grain boundaries on thermal conductivity are calculated. Results show that the splat interface influences the thermal conductivity of the TBCs. Those results provide important guidance for reducing the thermal conductivity of thermal barrier coatings.
Highlights
Thermal barrier coatings (TBCs), an oxide ceramic layer for the protection of a substrate material, are widely used for the thermal, oxidation and hot corrosion protection of high-temperature components in gas turbines [1]
The results revealed that more interface, higher porosity and more interlamellar pores can reduce the thermal conductivity of TBCs
The finite element (FE) model was established based on electron backscatter diffraction (EBSD) analysis, which could offer more microstructure information
Summary
Thermal barrier coatings (TBCs), an oxide ceramic layer for the protection of a substrate material, are widely used for the thermal, oxidation and hot corrosion protection of high-temperature components in gas turbines [1]. To research the relationship between interface and thermal conductivity, the model of heat conduction established by McPherson [11], the model of object oriented finite (OFF) established by Wang et al [12] and the mathematical formula that can calculate the influence of the interface on thermal conductivity established by Wei and his colleagues [13] all made explanations for low thermal conductivity of the coatings with the lamellae They think that the lamellar interspaces are equivalent to the pores parallel to the interface and that the width of the pores is equivalent to the average free path of the gas molecules, which limits the conduction of heat flow. The effect coefficient of grain boundaries, interfaces and monoclinic phase on thermal conductivity are directly calculated; it provides a reference for how to guide the spraying process to lower the thermal conductivity of the coatings
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