Abstract: The continuous rise in turbine inlet temperatures in aero-engines has intensified the need for improved thermal insulation in thermal barrier coatings (TBCs). Traditionally, reducing the thermal conductivity of TBCs has been the primary strategy to enhance their thermal insulation. Columnar TBCs are generally deemed to have higher thermal conductivity and inferior thermal insulation compared to lamellar TBCs. However, in this study, we demonstrate that under ultra-high temperature conditions (>1300 °C), columnar TBCs exhibit superior radiative cooling capabilities due to their higher emissivity in the near-infrared region. This enhanced radiative heat dissipation effectively offsets the limitations of their high thermal conductivity. A novel "blackbody effect" hypothesis is proposed to elucidate this behavior. Finite element simulations quantitatively substantiate this hypothesis, showing strong agreement with experimental observations. These findings offer a groundbreaking perspective: columnar coatings, despite higher thermal conductivity, can narrow the thermal insulation gap with lamellar coatings at ultra-high temperatures through enhanced radiation cooling capabilities. This work provides a new structural strategy for optimizing emissivity and broadens the design framework for next-generation TBCs.

Key words: Infrared emissivity, Radiative cooling, Finite element method, Structure optimization, Thermal barrier coatings