Microstructural evolution of high purity alumina ceramics prepared by a templated grain growth method

Textured alpha-alumina ceramics were prepared by mixing different ratios of three-sized plate-like alpha-alumina particles and fine equiaxed particles without the use of sintering aids. The plate-like particles have developed a-b planes and were incorporated as an aligned template. Mixed powders were formed into a green sheet using a doctor blade technique and sintered under various conditions (temperature, duration and atmosphere). The development of microstructure and texture in the sintered bodies was examined and correlated with the preparation conditions. The addition of plate-like particles to the fine equiaxed powder suppressed densification and grain growth during sintering. The plate-like particles tend to grow with a lower aspect ratio at high temperatures, especially under vacuum sintering conditions. The addition of 30% plate-like particles produced sintered bodies with the highest uniaxial < 001 > orientation, but with residual porosity. The addition of 5% plate-like particles resulted in sintered bodies with almost full density but texture development was inferior to that of 30%. The vacuum-sintered specimens with larger amounts of platelets exhibited pseudo-isotropic grain growth and high-to-medium uniaxial < 001 > orientation, which suggests that anisotropic grain growth is not essential to achieve a high degree of orientation. (C) 2016 The Ceramic Society of Japan. All rights reserved.