Effect of carbon content on electrical, thermal, and mechanical properties of pressureless sintered SiC ceramics

Abstract This study investigates the influence of carbon content, ranging from 2.5 to 13.0 wt.%, on the electrical, thermal, and mechanical properties of pressureless sintered SiC ceramics sintered with 0.8 wt.% B 4 C. The results indicate a substantial decrease in electrical resistivity from 4.7 × 10 2 to 9.1 × 10 −2 Ω cm, particularly when carbon content exceeds 7.0 wt.%, which is attributed to the formation of a conductive network. Thermal conductivity decreased from 151.6 to 116.5 W m −1  K −1 due to increased phonon scattering, a higher carbon volume fraction, and increased porosity. The maximum flexural strength and hardness, 384.0 MPa and 29.1 GPa, respectively, are observed at 4.0 wt.% carbon, followed by a decline at higher carbon content. Fracture toughness improved from 2.7 to 3.8 MPa m 1/2 with increasing carbon content due to enhanced crack deflection. At 10.0 wt.% carbon, the recorded properties include electrical resistivity of 9.3 × 10 −1 Ω cm, thermal conductivity of 129.9 W m −1  K −1 , flexural strength of 226.2 MPa, fracture toughness of 3.6 MPa m 1/2 , and hardness of 21.8 GPa.