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

Abstract

Pure b-Si 3 N 4 is used in the present work as the starting powder to synthesize a-sialon (a ) ceramics; 5 wt.% a -seeds are added to promote nucleation of a-sialon. Transmission electron microscopy (TEM) observations reveal an inhomogeneous microstructure in which intergranular precipitates are produced in some regions where the structure and the chemistry of the interfaces vary significantly. The surfaces of the sialon grains adjacent to the precipitates are always rounded and corrugated, and the interfacial 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-controlled kinetics. The increased number of growth sites eventually gives rise to a corrugated surface.