A comparative assessment of thermal conductivity of functionally graded and equivalent non-graded ZrB2–B4C–SiC–LaB6 ultra-high-temperature ceramic composites

In this study, functionally graded ZrB₂–B₄C–SiC–LaB₆ composite materials (FGMs) with potential applications in hypersonic aircraft thermal protection systems were fabricated using spark plasma sintering. A systematic study of the thermal conductivity of the FGM, the conductivity of respective FGM layers, and the equivalent non-graded composites, was performed from room temperature up to 450 °C. The results suggest that the thermal conductivity of the FGMs (in the through-thickness direction) and their equivalent non-graded composites ranged between 25 and 34.9 W/mK, which was ∼60 % less than ZrB₂. While the overall thermal conductivity of the FGM and equivalent non-graded composites were similar, in the FGM, the topmost layer with high ZrB₂-content displayed up to 245 % higher thermal conductivity than the bottom layer with high B₄C content. A systematic comparison between experimentally determined conductivity and relevant thermal conductivity models was conducted.