Orientation-dependent properties of silicon nitride with aligned reinforcing grains

Silicon nitride with the aligned reinforcing grains was prepared by tape ca sting with addition of the silicon nitride whiskers and gas-pressure sinter ing at 2148 K. The microstructure and the mechanical properties of the sint ered sample, including the fracture toughness and the three-point flexural strength, were highly anisotropic. Both the fracture toughness and the flex ural strength were the highest when the crack-propagation direction was nor mal to the alignment direction. This result was interpreted from the lamina te 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 wer e not the fracture origins.