The effect of in situ synthesized AlN on densification of SiC ceramics by pressureless sintering

This study reports the influence of in situ synthesized AlN on the densification of SiC ceramic by pressureless sintering. Pore-free dense SiC ceramics were achieved by sintering at 2170 °C for 1 h with 4 wt% in-situ AlN and 3 wt% carbon as sintering additives. AlN was synthesized through a carbothermal reduction reaction with Al2O3 and carbon in N2 at 1700 °C for 4 h. The reaction process of the powders and densification mechanism for SiC ceramic were also investigated. The densification behavior of SiC ceramics was found to be greatly promoted by in situ introduction of AlN. The as-sintered SiC ceramics presented homogenous microstructure with clean grain boundaries and exhibited transgranular fracture mode, indicating a strong bonding between silicon carbide grains. The flexural strength and fracture toughness of the sintered samples were 394±48 MPa and 3.07±0.20 MPa m1/2, respectively.