Microstructure Characterization of Gas‐Pressure‐Sintered β‐Silicon Nitride Containing Large β‐Silicon Nitride Seeds

Abstract

Fine β‐Si 3 N 4 powders with or without the addition of 5 wt% of large β‐Si 3 N 4 particles (seeds) were gas‐pressure sintered at 1900°C for 4 h using Y 2 O 3 and Al 2 O 3 as sintering aids. The microstructures were examined on polished and plasmaetched surfaces. These materials had a microstructure of in situ composites with similar small matrix grains and different elongated grains. The elongated grains in the materials with seeds had a larger diameter and a smaller aspect ratio than those in the materials without seeds. A core/rim structure was observed in the elongated grains; the core was pure β‐Si 3 N 4 and the rim was β‐SiAION. These results show that the large β‐Si 3 N 4 particles acted as seeds for abnormal grain growth and the rim was formed by precipitation from the liquid containing aluminum.