The effect of fabrication parameters on the mechanical properties of sintered reaction bonded porous Si3N4 ceramics

Porous silicon nitride ceramics were prepared via sintered reaction bonded silicon nitride at 1680 degrees C. The grain size of nitrided Si3N4 and diameter of post-sintered beta-Si3N4 are controlled by size of raw Si. Porosity of 42.14-46.54% and flexural strength from 141 MPa to 165 MPa were obtained. During post-sintering with nano Y2O3 as sintering additive, nano Y2O3 can promote the formation of small beta-Si3N4 nuclei, but the large amount of beta-Si3N4 (>20%) after nitridation also works as nuclei site for precipitation, in consequence the growth of fine beta-Si3N4 grains is restrained, the length is shortened, and the improvement on flexural strength is minimized. The effect of nano SiC on the refinement of the beta-Si3N4 grains is notable because of the pinning effect, while the effect of nano C on the refinement of the beta-Si3N4 grains is not remarkable due to the carbothermal reaction and increase in viscosity of the liquid phase. (C) 2014 Elsevier Ltd. All rights reserved.