Thermal conductivity and thermal shock resistance of TiB₂-based UHTCs enhanced by graphite platelets

TiB₂-SiC-C and TiB₂-TiC-C heteromodulus ceramics were sintered by reactive hot pressing of TiC-B₄C-Si and TiC-B₄C precursors at 1830 °C and 30 MPa. Sintering time at the maximum temperature was between 2 and 8 min. The reactions in TiC-B₄C-Si green body create submicron (100–400 nm) TiB₂ crystals inside silicon carbide grains as well as B_xSi_yC_z nanofibers, which nucleate near SiC surfaces. Low hardness graphite platelets are formed within the hard matrix during the in-situ exothermic reaction. “Soft-hard” grain combination produces substantially improved fracture toughness (up to 9 MPa m^1/2). The materials also demonstrate high thermal conductivity (up to 120 W/m∙K) and high thermal shock resistance. The thermal shock crack growth is arrested by the graphite platelets.