EVOLUTION OF GRAIN-BOUNDARY FILMS IN LIQUID-PHASE SINTERED SILICON-NITRIDE DURING HIGH-TEMPERATURE TESTING

Transmission electron microscopy (TEM) is used to study the effect of high-temperature tests on the amorphous grain boundary films in a comm ercial, liquid phase sintered silicon nitride ceramic. The thickness o f amorphous films between silicon nitride grains is characterized by h igh-resolution TEM. In addition, electron energy-loss spectroscopy is applied to analyze the composition of grain boundary films. A smaller equilibrium film thickness is measured in the specimens after testing. This decrease in film thickness is due to changes in the intergranula r film chemistry. The composition changes are caused by phase transfor mations in the secondary crystalline phases, which were observed by TE M and X-ray diffraction, and by crystallization of residual amorphous pockets during high-temperature testing. (C) 1998 Acta Metallurgica In c. Published by Elsevier Science Ltd. All rights reserved.