Mechanical properties of fine-grained silicon nitride ceramics

Abstract

Mechanical properties and microstructures of both fine-grained β-silicon nitride ceramics and annealed materials were examined. The microstructure of fine-grained β-silicon nitride ceramics has fine and uniform grains. After annealing, fine and rod-like grains have been developed. Fracture toughness and bending strength of fine-grained β-silicon nitride ceramics increased by the annealing. The increased mechanical properties are related to the microstructural change during the annealing. Further, SEM and EDS analyses made clear that the size of flaw in samples were over 10 times of average diameters of the grains. The fracture origin changed from large suicide particles to smaller pores by annealing under high nitrogen pressure.