TEM Analysis of Core/Rim Structure in β-Silicon Nitride Ceramics

Abstract

Fine β-Si3N4 powders containing 5mass% of large β-Si3N4 particles were gas-pressure sintered at 1900°C for 4h using Y2O3 and Al2O3 as sintering aid. A core/rim structure was observed by scanning and transmission electron microscopy. The core was pure β-Si3N4 and the rim was β-sialon. The electron dffraction patterns indicated that the core and rim had the same orientation, showing that the rim was epitaxially grown on the core. Lattice mismatch was observed at the core/rim boundary by HREM. These results show that the relatively large β-Si3N4 particles in raw material powder acted as seeds for grain growth and that the rim was formed by epitaxial precipitation from liquid containing Al. When β-Si3N4 is used as the raw material powder, the particle size distribution is especially important for the development of in-situ composite microstructure.