K. Hirao et al., MICROSTRUCTURE CONTROL OF SILICON-NITRIDE BY SEEDING WITH RODLIKE BETA-SILICON NITRIDE PARTICLES, Journal of the American Ceramic Society, 77(7), 1994, pp. 1857-1862
The effect of seeding on microstructure development and mechanical pro
perties of silicon nitride was investigated by the use of morphologica
lly regulated rodlike beta-Si3N4 single-crystal particles with a diame
ter of 1 mum and a length of 4 mum as seed crystals. Silicon nitride w
ith a bimodal microstructure was fabricated under a relatively low nit
rogen gas pressure of 0.9 MPa owing to the epitaxial growth of beta-si
licon nitride from the seed particles. Grain growth from seeds followe
d the empirical equation D(n) - D0n = kt, with growth exponents of 3 a
nd 5 for the c-axis direction and the a-axis direction, respectively,
being analogous to the kinetics of matrix grain growth. By seeding mor
phologically regulated particles, fracture toughness of silicon nitrid
e was improved from 6.3 to 8.4-8.7 MPa . m1/2, retaining high strength
levels of about 1 GPa.