Influences of intergranular precipitates on the structure and chemistry ofinterface in silicon nitride materials

Pure beta -Si3N4 is used in the present work as the starting powder to synt hesize alpha -sialon (alpha') ceramics; 5 wt.% alpha'-seeds are added to pr omote nucleation of cu-sialon. Transmission electron microscopy (TEM) obser vations reveal an inhomogeneous microstructure in which intergranular preci pitates are produced in some regions where the structure and the chemistry of the interfaces vary significantly. The surfaces of the sialon grains adj acent to the precipitates are always rounded and corrugated, and the interf acial thickness increases. An internal band structure is usually discovered in these grains. Chemical analyses find that a small number of Y ions have been incorporated into the surface lattice. A possible formation mechanism of the corrugated surface is proposed and suggests a redissolution process of sialon grains during the crystallization of intergranular precipitates and an enhanced growth during cooling that is governed by interface-control led kinetics. The increased number of growth sites eventually gives rise to a corrugated surface. Copyright (C) 2001 John Wiley & Sons, Ltd.