Relationship between microstructure and mechanical performance of a 70% silicon nitride-30% barium aluminum silicate self-reinforced ceramic composite

The abnormal grain growth of beta -Si3N4 was observed in a 70% Si3N4-30% ba rium aluminum silicate (70%-Si3N4-30%-BAS) self-reinforced composite that w as pressureless-sintered at 1930 degreesC; Si3N4 starting powders with a wi de particle-size distribution were used. The addition of coarse Si3N4 powde r encouraged the abnormal growth of beta -Si3N4 grains, which allowed micro structural modification through control of the content and size distributio n of beta -Si3N4 nuclei. The mechanical response of different microstructur es was characterized in terms of flexural strength, as well as Indentation Fracture resistance, at room temperature. The presence of even a small amou nt of abnormally grown beta -Si3N4 grains improved the fracture toughness a nd minimized the variability in flexural strength.