Abstract
HfB2-ZrB2 based ultra-high temperature ceramics (UHTCs) are used as protective tiles for nose cones and leading edges of the hypersonic vehicles that face harsh service conditions of temperatures >2000 °C. The present work assesses the effect of SiC (20 vol.%) and carbon nanotubes (CNT, 6 vol.%) incorporation on isolating the phononic and electronic contribution to thermal conductivity of spark plasma sintered HfB2-ZrB2 based UHTCs. Except HfB2-SiC, all ZrB2 based UHTC composites elicited similar electrical conductivity (∼ 5.7 × 106 S/m), whereas a marginal increase of ∼9% in thermal conductivity was observed with CNT reinforcement in HfB2-ZrB2–SiC composites. With HfB2/ZrB2-SiC composites eliciting high thermal conductivity (120–150 Wm-1K-1), the current work emphasizes the domination of phononic scattering (by ∼44%) due to solid solutioning in HfB2-ZrB2-based ceramics. Further, electronic thermal scattering events may only be marginal at interfaces of CNT and ZrB2, and limit thermal scattering in HfB2/ZrB2-SiC-CNT based UHTCs for hypersonic applications.
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