Influence of additive content on the anisotropy in hot-pressed Si 3N 4 ceramics using grain orientation measurements

Abstract

The influence of additive content on the microstructure and its mechanical properties in planes parallel and normal to the hot-pressing axis of Si 3N 4 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-Si 3N 4 grains in the plane parallel to the hot-pressing direction.