Effect of annealing on mechanical properties of silicon carbide sintered with aluminum nitride and scandium oxide

Beta-SiC powder samples containing 1 wt.% α-SiC as a seed and 10 vol.% AlN-Sc2O3 as a sintering additive were hot-pressed at 1900 °C for 1 h and subsequently annealed at 2000 °C for 1 h, 3 h and 6 h. When the annealing time was increased, the microstructure changed from equiaxed to elongated grains, which resulted in a self-reinforced microstructure consisting of elongated grains (hexagonal platelet grains in 3-dimensions). The development of a self-reinforced microstructure resulted in significant improvement in toughness. However, the improved toughness was offset by a reduction in strength. The typical fracture toughness and strength of the ceramics annealed for 6 h were 7.3 MPa·m1/2 and ∼500 MPa, respectively.