MICROSTRUCTURE AND DISTRIBUTION OF IMPURITIES IN HOT-PRESSED AND SINTERED SILICON NITRIDES

Two hot‐pressed (HS 130 and NC 132) and two sintered silicon nitrides (with MgO·Al2O3 and Y2O3 additives) were examined in detail by X‐ray diffraction, emission spectroscopy, medium‐and high‐resolution electron microscopy, and X‐ray microanalysis. The overall morphologies of the four materials are quite comparable. Very thin (10 to 20 Å) intergranular glassy films were detected in all the materials at almost all grain and interphase boundaries. The composition of these glasses was determined by X‐ray microanalysis using a 200‐Å electron probe and the softening temperature was estimated from available phase diagrams. The results are in good agreement with the known softening temperatures for the four silicon nitrides, thereby confirming the central role played by glassy phases in determining the high‐temperature mechanical properties of these materials. Copyright © 1979, Wiley Blackwell. All rights reserved