Microstructural Control for Strengthening of Silicon Carbide Ceramics

Fine-grained (<1 μm) silicon carbide ceramics with high strength were obtained by using ultrafine (～90 nm) β-SiC starting powders and a seeding technique for microstructural control. The microstructures of the as-hot-pressed and annealed ceramics without α-SiC seeds consisted of fine, uniform, and equiaxed grains. In contrast, the annealed material with seeds had a uniform, anisotropic microstructure consisting of elongated grains, owing to the overgrowth of β-phase on α-seeds. The strength, the Weibull modulus, and the fracture toughness of fine-grained SiC ceramics increased with increasing grain size up to ～1 μm. Such results suggested that a small amount of grain growth in the fine grained region (<1 μm) was beneficial for mechanical properties. The flexural strength and the fracture toughness of the annealed seeded materials were 835 MPa and 4.3 MPa·m^1/2, respectively.