Microstructure and ambient properties of a Sialon composite prepared by hot pressing and reactive sintering of β–Si3N4 coated with Al2O3

Abstract

A composite microstructure, consisting of β-Sialon, O-Sialon, and X-Sialon phases was produced by coating β–Si3N4 particles with amorphous alumina followed by hot pressing and reactive sintering at 1923 K. The particle coating procedure was selected over conventional powder blending in order to promote heterogeneous nucleation of β-Sialon grains on β–Si3N4 particles uniformly. The microstructure, chemistry of the phases, and interphase interfaces of this ceramic were characterized by transmission electron microscopy (TEM) and high-resolution analytical electron microscopy (AEM). Both electron energy-loss spectroscopy (EELS) and energy-dispersive spectroscopy (EDS) x-ray microanalysis in AEM revealed that b-Sialon grains had varying aluminum and oxygen contents. High-resolution electron microscopy (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 of high temperature properties. The fracture toughness and wear properties were evaluated at room temperature. Available data indicate that the fracture toughness and wear of β-Sialon composite can be significantly improved by the powder coating technique compared to the conventional powder blending technique.