Mechanical Properties of Silicon Nitride with Anisotropic Microstructure

Abstract

Silicon nitride with anisotropic microstructure was fabricated by tape-casting of raw powder slurries with 0-10vol% seed particles of morphologically regulated β-Si3N4 single crystal, followed by gas pressure sintering of stacked sheets. The effect of orientation degree and area fraction of large elongated grains on mechanical properties was studied. Fracture toughness (KIC) and bending strength (σf) measured in the direction perpendicular to grain alignment increased with an increase in seeds amount, which was associated with the fact that both orientation degree and area fraction of large elongated grains increased with increasing amount of seeds. The specimen with 5vol% seeds, in which large elongated grains occupy a cross-sectional area of about 46%, exhibited a dominant orientation parallel to the casting direction. The specimen showed high KIC of 11.7MPa·m1/2 and high σf of 1200MPa. Further addition of seeds resulted in a slight decrease in KIC and σf owing to pore generation and coalescense of large elongated grains. On the contrray, KIC and σf measured in the direction parallel to the grain alignment decreased monotonously with an increase in seeds amount.