Porous Si3N4 ceramics with varied porosities were prepared by liquid phase sintering of fibrous α-Si3N4 powder with different morphology after ball milling. The influence of the ball milling time on porosity, shrinkage, microstructure and mechanical properties of Si3N4 ceramics were investigated. With increasing of the ball milling time from 0 h to 24 hrs, the mean length and aspect ratio of the fibrous α-Si3N4 particles decreased dramatically, resulting in the porosity of porous Si3N4 ceramics decreased from 55.6% to 19.3%. With the decreased length of the fibrous α-Si3N4 particles, microstructures with decreased aspect ratio of β-Si3N4 grains were formed, as a result of increased nuclei number and limited grain growth of the β-Si3N4 grains. The flexural strength varied from 62 MPa to 205 MPa could be obtained attributed to the synergy effect of porosity and microstructure.

Keywords: Fibrous α-Si3N4, Porous ceramics, Porosity, Flexural strength.