Mechanical properties of silicon nitrides with tailored microstructure by seeding

The effect of seeding on microstructure development and mechanical properties of silicon nitride was investigated by the use of two kinds of morphologically regulated beta-Si3N4 single crystal particles, Silicon nitrides with bimodal grain-size distribution were obtained by seeding, The seeding of an appropriate amount of beta-Si3N4 particles with an appropriate size allowed the development of optimal microstructures, where large elongated grains grown from the seed particles were highly dispersed, As a result, fracture toughness increased retaining the high strength levels of about 1 GPa, On the other hand, specimens with large amount of seed particles presented lower strength owing to the coalescence of large elongated grains. The increase in fracture toughness can be associated with diameter as well as volume fraction of well dispersed large beta-Si3N4 grains, assuming toughening by the bridging mechanism.