Preparation of Porous Si3N4 Ceramics with Controlled Porosity and Microstructure by Fibrous α‐Si3N4 Addition

Abstract

Porous silicon nitride ceramics with various porosities were fabricated by liquid phase sintering of mixtures containing fibrous and equiaxed α‐Si3N4 powder with a various content ratios. The effects of the contents of the fibrous α‐Si3N4 powder (0%–100%) on the microstructure and mechanical properties of porous Si3N4 ceramics were studied. As the increase of the fibrous α‐Si3N4 powder content, both the density of green bodies and the linear shrinkage decreased, resulting in increased porosity due to the inhibited densification by the fibrous Si3N4 particle. XRD analysis proved the complete formation of single β‐Si3N4 phase. SEM analysis revealed that the microstructure of the low content of fibrous α‐Si3N4 porous ceramics was almost composed of fine elongated β‐Si3N4 grains with high aspect ratio while numerous coarse elongated β‐Si3N4 grains with low aspect ratio surrounding fine grains were formed as the content of the fibrous α‐Si3N4 powder increased. With the increase in content of the fibrous α‐Si3N4 powder from 0% to 100%, the porosity changed from 47.8% to 56.6%, and the flexural strength decreased from 146 to 62 MPa correspondingly, indicating a flexural adjustment of the porosity and mechanical properties.