Orientation-dependent properties of silicon nitride with aligned reinforcing grains

Silicon nitride with the aligned reinforcing grains was prepared by tape casting with addition of the silicon nitride whiskers and gas-pressure sintering at 2148 K. The microstructure and the mechanical properties of the sintered sample, including the fracture toughness and the three-point flexural strength, were highly anisotropic. Both the fracture toughness and the flexural strength were the highest when the crack-propagation direction was normal to the alignment direction. This result was interpreted from the laminate composite materials' point of view. Although the large elongated grains were as long as 44.4 +/- 12 mu m and as wide as 5.1 +/- 0.67 mu m, they were not the fracture origins.