Effect of Sintering Additives on Microstructure and Mechanical Properties of Porous Silicon Nitride Ceramics

Abstract

Porous silicon nitride (Si3N4) ceramics with about 50% porosity were fabricated by pressureless sintering of α‐Si3N4 powder with 5 wt% sintering additive. Four types of sintering aids were chosen to study their effect on the microstructure and mechanical properties of porous Si3N4 ceramics. XRD analysis proved the complete formation of a single β‐Si3N4 phase. Microstructural evolution and mechanical properties were dependent mostly on the type of sintering additive. SEM analysis revealed the resultant porous Si3N4 ceramics as having high aspect ratio, a rod‐like microstructure, and a uniform pore structure. The sintered sample with Lu2O3 sintering additive, having a porosity of about 50%, showed a high flexural strength of 188 MPa, a high fracture toughness of 3.1 MPa·m1/2, due to fine β‐Si3N4 grains, and some large elongated grains.