PROCESSING STRATEGY FOR PRODUCING HIGHLY ANISOTROPIC SILICON-NITRIDE

Silicon nitride with a preferred orientation of large elongated grains was obtained by tape casting of raw powder slurry seeded with rodlike beta-Si3N4 particles, followed by a gas pressure sintering under 1 MP a nitrogen pressure. The large elongated grains developed from seeds l ay in planes parallel to the casting direction in a two-dimensional di stribution. Increased fracture toughness (11.1 MPa . m(1/2)) and bendi ng strength (1100 MPa) were achieved in the direction perpendicular to the grains alignment compared to specimens with a random distribution of elongated grains. Moreover, the specimens exhibited a high Weibull modulus of 46 due to the uniform distribution of large grains.