Microstructure Control of Silicon Nitride by Seeding with Rodlike β‐Silicon Nitride Particles

The effect of seeding on microstructure development and mechanical properties of silicon nitride was investigated by the use of morphologically regulated rodlike β‐Si 3 N 4 singlecrystal particles with a diameter of 1 μm and a length of 4 μm as seed crystals. Silicon nitride with a bimodal microstructure was fabricated under a relatively low nitrogen gas pressure of 0.9 MPa owing to the epitaxial growth of β‐silicon nitride from the seed particles. Grain growth from seeds followed the empirical equation D n –D 0 n = kt , with growth exponents of 3 and 5 for the c ‐axis direction and the a ‐axis direction, respectively, being analogous to the kinetics of matrix grain growth. By seeding morphologically regulated particles, fracture toughness of silicon nitride was improved from 6.3 to 8.4–8.7 MPa·m 1/2 , retaining high strength levels of about 1 GPa.