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

<jats:p> Detailed microstructural analysis of a 10 mol% Y <jats:sub>2</jats:sub> O <jats:sub>3</jats:sub> fluxed hot‐pressed silicon nitride reveals that, in addition to the yttrium‐silicon oxynitride phase located at the multiple Si <jats:sub>3</jats:sub> N <jats:sub>4</jats:sub> 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 <jats:sub>2</jats:sub> Si(Si <jats:sub>2</jats:sub> O <jats:sub>3</jats:sub> N <jats:sub>4</jats:sub> ), 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 <jats:sub>3</jats:sub> N <jats:sub>4</jats:sub> grains enveloped by Y <jats:sub>2</jats:sub> Si(Si <jats:sub>2</jats:sub> O <jats:sub>3</jats:sub> N <jats:sub>4</jats:sub> ), suggests that densification occurred by a liquid‐phase “solution‐reprecipitation” process. </jats:p>