Electrical, thermal and mechanical properties of silicon carbide–silicon nitride composites sintered with yttria and scandia

Composites of SiC–Si3N4, which consisted of uniformly distributed β-Si3N4 grains, nitrogen-doped β-SiC grains, and a Y- and Sc-containing junction phase, were fabricated by conventional hot-pressing in nitrogen atmosphere, with a new additive system of 2 vol% equimolar Y2O3–Sc2O3 additives. The effect of Si3N4 content on the electrical, thermal, and mechanical properties of SiC–Si3N4 composites were investigated. The electrical resistivity showed a minimum at 10 vol% Si3N4 content, owing to the growth of nitrogen-doped SiC grains from a Y–Sc–Si oxycarbonitride glass via a solution-reprecipitation mechanism. The thermal conductivity decreased with increasing Si3N4 content, whereas the fracture toughness increased with increasing Si3N4 content. Typical electrical resistivity and thermal conductivity of the SiC–10 vol% Si3N4 composites were 0.09 Ω cm and 83 W/m K at room temperature, respectively. The flexural strength, fracture toughness, and Vickers hardness values of the SiC–35 vol% Si3N4 composite were ∼720 MPa, ∼7 MPa m1/2, and ∼19 GPa, respectively.