Microstructure of a sialon composite prepared by hot pressing and reactive sintering of β-Si3N4 coated with amorphous Al2O3

A composite microstructure, consisting of beta-sialon, O-sialon and X-sialon phases, was produced by coating beta-Si3N4 particles, with amorphous alumina followed by hot pressing and reactive sintering at 1923 K. The microstructure, chemistry of the phases and interphase interfaces of this ceramic were characterized by TEM and high resolution AEM. Both polyhedral and elongated beta-sialon grains were observed. TEM examination showed the formation of a large number of beta-sialon grains and PEELS and EDS X-ray microanalysts in AEM revealed they had varying amounts of aluminum and oxygen contents. HREM examination of several interphase interfaces and triple junctions suggests that the amount of glassy phase in the produced ceramic is substantially lower compared to those reported in the literature. This is of importance for high temperature properties. (C) 1999 Elsevier Science Ltd. and Techna S.r.l. All rights reserved.