Microstructure of Y ₂ O ₃ Fluxed Hot‐Pressed Silicon Nitride

Abstract

Detailed microstructural analysis of a 10 mol% Y 2 O 3 fluxed hot‐pressed silicon nitride reveals that, in addition to the yttrium‐silicon oxynitride phase located at the multiple Si 3 N 4 grain junctions, there is a thin boundary phase 10 to 80 Å wide separating the silicon nitride and the oxynitride grains. Also, X‐ray microanalysis from regions as small as 200 Å across demonstrates that the yttrium‐silicon oxynitride, Y 2 Si(Si 2 O 3 N 4 ), phase can accommodate appreciable quantities of Ti, W, Fe, Ni, Co, Ca, Mg, Al, and Zn in solid solution. This finding, together with observations of highly prismatic Si 3 N 4 grains enveloped by Y 2 Si(Si 2 O 3 N 4 ), suggests that densification occurred by a liquid‐phase “solution‐reprecipitation” process.