Influence of additive content on the anisotropy in hot-pressed Si3N4 ceramics using grain orientation measurements

The influence of additive content on the microstructure and its mechanical properties in planes parallel and normal to the hot-pressing axis of Si3N4 ceramics has been investigated by direct measurement of the grain orientation from SEM micrographs and orientated Vicker’s indentations. It is shown that an increasing additive content leads to a microstructure with grains of higher aspect ratios, resulting in an increase of the fracture toughness. Furthermore, the difference in mechanical anisotropy between the planes parallel and normal to the hot-pressing directions is gradually reduced with increasing additive content, due to the smaller degree of orientation of the elongated β-Si3N4 grains in the plane parallel to the hot-pressing direction.