MECHANICAL-PROPERTIES OF SILICON-NITRIDE WITH ANISOTROPIC MICROSTRUCTURE

Silicon nitride with anisotropic microstructure was fabricated by tape -casting of raw powder slurries with 0-10 vol% seed particles of morph ologically regulated beta-Si3N4 Single crystal, followed by gas pressu re sintering of stacked sheets, The effect of orientation degree and a rea fraction of large elongated grains on mechanical properties was st udied, Fracture toughness (K-IC) and bending strength (sigma(t)) measu red in the direction perpendicular to grain alignment increased with a n increase in seeds amount, which was associated with the fact that bo th orientation degree and area fraction of large elongated grains incr eased with increasing amount of seeds, The specimen with 5 vol% seeds, in which large elongated grains occupy a cross-sectional area of abou t 46%, exhibited a dominant orientation parallel to the casting direct ion. The specimen showed high K-IC of 11.7 MPa . m(1/2) and high sigma (f) of 1200 MPa. Further addition of seeds resulted in a slight decrea se in fire and of owing to pore generation and coalescense of large el ongated grains. On the contrray, K-IC and sigma(f) measured in the dir ection parallel to the grain alignment decreased monotonously with an increase in seeds amount.