Crossover of thermal conductivity in SiC-reinforced ZrB 2 –HfB 2 composites at elevated temperatures

Ultra-high temperature ceramics, especially di-borides, are regarded as potential candidates for thermal protection system in hypersonic vehicles by virtue of their high thermal conductivity. However, studies on thermal conductivity behaviour of ultra-high temperature ceramic di-borides exhibit scattered data at high temperatures. Herein, we report a systematic study of a range of di-boride compositions aiming at multiple aspects including the effect of temperature on thermal conductivity of monolithic di-borides (ZrB 2 and HfB 2 ), effect of SiC and carbon nanotubes (CNTs) addition on ZrB 2 and HfB 2 with increasing temperature till 1200 °C, and effect on thermal conductivity with systematic incorporation of ZrB 2 and HfB 2 into each another. Highest experimental thermal conductivity (63–83 W m −1 K −1 ) observed in 20 vol% SiC reinforced ZrB 2 composite (in the temperature range of 50–1200 °C) witnessed crossover (and drop) than that of monolithic sample (above 900 °C) due to increased phonon–phonon scattering in SiC with the rise in temperature. Concurrently, agglomerated CNT reinforcement further decreased thermal conductivity due to increased inhomogeneity in solid solutioning and enhanced phonon scattering. Graphical abstract