IAM - Ceramic Materials and Technologies

Model experiments concerning abnormal grain growth in silicon nitride

  • Author: Dressler, W.; Kleebe, H. J.; Hoffmann, M. J.; Ruhle, M.; Petzow, G.
  • Source: JOURNAL OF THE EUROPEAN CERAMIC SOCIETY 16 (1996), 1, 3–14
  • Model experiments concerning abnormal grain growth in silicon nitride.

Abstract

Model experiments were designed to study abnormal grain growth in Si3N4-based ceramics. Experiments relating inhomogeneous crystalline secondary-phase distribution to exaggerated grain growth conclusively showed that abnormal grain growth is not governed by secondary-phase distribution, because a rapid homogenization of locally formed liquid occurs via capillary forces. Further investigations were focussed on intrinsic properties of the alpha-Si3N4-starting powders. The influence of: (i) beta-Si3N4-grain morphology; (ii) beta-Si3N4-nuclei density, and (iii) beta-Si3N4-grain-size distribution of the powder blends on microstructural development were analyzed. The results revealed that a large basal plane of beta-Si3N4 seeds energetically and kinetically favours grain growth. However, this effect is only partly responsible for abnormal grain growth. The formation of elongated Si3N4 grains, such as in in situ reinforced Si3N4 materials, strongly depend on the amount and grain-size distribution of beta-Si3N4 nuclei present in the alpha-Si3N4-starting powder.