Low-temperature fabrication of conductive SiC ceramics using SiO₂-coated SiC nanopowder with Sc₂O₃ additive by spark plasma sintering

To reduce the sintering temperature of liquid-phase sintered conductive SiC ceramics, the SiC nanopowder with Sc₂O₃ additives was intentionally oxidized by heat treatment in air to enhance the SiO₂ content coated on SiC surfaces moderately. Taking advantage of the lower eutectic temperature (1660 °C) between SiO₂ and Sc₂O₃, conductive SiC ceramics were successfully sintered at 1700 °C. The effects of sintering temperature (1700–1900 °C), holding time (1–10 min), and additive content (1–7 wt.%) on microstructural, mechanical, and electrical properties were systematically investigated. The phase composition of as-received SiC ceramics contained Sc–Si–O–C–N and doped β-SiC, without apparent phase transformation of β-SiC to α-SiC. The Vickers hardness, elastic modulus, and fracture toughness of SiC ceramics varied within the ranges of 18.08–22.29 GPa, 269.12–391.16 GPa, and 4.09–7.86 MPa m^1/2, respectively. The electrical resistivity of conductive SiC ceramics obtained under different process conditions varied in a small range (1–10 Ω cm). Meanwhile, the low-temperature sintering, phase formation, and evolution mechanisms of electrical properties were discussed in detail.