Evaluation of Grain Orientation in Textured b-Si3N4 Ceramics with High Thermal Conductivity by Electron Microscopy

by Hiromi Nakano, Hiroshi Nakano, & Koji Watari AZojomo, 2 May 2006 b-Si₃N4 ceramics with highly oriented grains shows high thermal conductivity along the tape-casting direction. In order to clearly understand the relationship between microstructure and thermal conductivity in ceramics, we determined the degrees of orientation for each grain and the grain boundary. This work focuses on highly oriented b-Si₃N4 ceramics obtained by tape-casting with seed particles, followed by hot-pressing and HIPing. The degree of grain orientation was determined by an electron diffraction method combined with an electron back-scattered diffraction method. Each grain was oriented within 20 degrees tilting angle from the [0001] axis in the TEM observed specimen. Furthermore, the relationship between the microstructural data and thermal data were compared and discussed for various types of Si₃N4 ceramics. In this case, the appearance of high anisotropic thermal conductivity was caused by crystallographic nature, grain features, and grain purity during a liquid-sintering process. Read more