Pressureless solid-state sintering of SiC ceramics with BN and C additives

This study proposes BN as a new sintering aid for pressureless solid-state sintering of SiC ceramics. The full densification of SiC ceramics for 0.5-2.7 wt% BN addition showed the composition tolerance of the newly developed ceramics. The electrical resistivity decreased by an order of magnitude (10(7)-> 10(6) Omega.cm) as BN content increased from similar to 0.5 to similar to 0.9 wt% because of the increased BN-derived B doping in the SiC lattice. A further increase in BN content had no significant effect on the electrical resistivity, which is attributed to the limited solubility of B in the SiC lattice. The thermal conductivity decreased with increasing BN content owing to increased phonon scattering at B-doped sites and the thermally insulating BN phase located at the grain boundaries. The fracture toughness increased with increasing BN content owing to interfacial debonding at the weak SiC-BN interfaces. However, intrinsically weak BN grains with low hardness were responsible for reduced flexural strength and hardness with increasing BN content.