Microstructure and mechanical properties of silicon nitride with tri-laminate structures

Silicon nitride ceramics with tri-laminate structures were prepared using two kinds of layers; layer with the aligned silicon nitride whisker seeds (named as “S” layer) and layer without the seed (“N” layer). The fracture toughness values on the casting surface of N layer of sample with a tri-laminate structure (N–S–N structure) showed an anisotropy, and this is contrary to the isotropic fracture toughness observed from the casting surface of sample consisting of only N layers. The fracture toughness anisotropy observed from N layer of the former sample is explained in terms of the microstructural anisotropy induced by the sintering shrinkage anisotropy within the casting plane.