Microstructure of Y2O3 Fluxed Hot‐Pressed Silicon Nitride

Abstract
Detailed microstructural analysis of a 10 mol% Y2O3 fluxed hot‐pressed silicon nitride reveals that, in addition to the yttrium‐silicon oxynitride phase located at the multiple Si3N4 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, Y2Si(Si2O3N4), 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 Si3N4 grains enveloped by Y2Si(Si2O3N4), suggests that densification occurred by a liquid‐phase “solution‐reprecipitation” process.

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