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.