Formation mechanism of an ultra-low thermal conductivity thermal barrier coating deposited using biomimetic hierarchical porous microspheres

The hierarchical porous microsphere is a promising feedstock for thermal barrier coatings (TBCs), due to its excellent flowability, high compression strength, and high temperature structure stability. This study aims to determine the formation mechanism of the coating deposited using hierarchical porous microspheres. For the (Sm 0.2 Gd0 .2 Dy 0.2 Er 0.2 Yb 0.2 ) 2 Zr 2 O 7 hierarchical microsphere sintered at 1000 ºC to 1550 ºC, the thermal conductivity increased from 0.21 to 0.64 W/m·K, the compression strength increased from 13 MPa to 80 MPa. The hierarchical porous structure can inhibit the heat flow from the surface to interior, resulting in the low melting degree in the plasma jet. Additionally, the coatings exhibit the characteristics of nanostructured coatings and hierarchical porous zones inherited from the microspheres, as evidenced by a comparison of compression strength and impact strength during deposition. The as-sprayed nanostructured coating shows a significantly lower initial thermal conductivity of 0.33 W/m·K at 1000 ºC compared to the conventional coating.