Silicon Nitride Based Ceramic Nanocomposites

Abstract

Nanocomposites (Si3N4/SiC) were studied by combined high‐resolution transmission electron microscopy and electron energy‐loss spectroscopic imaging (ESI) techniques. In ESI micrographs three types of crystalline grains were distinguished: Si3N4 matrix grains (0.5 μΩ), nanosized SiC particles (<100 nm) embedded in the Si3N4, and large SiC particles (100–200 nm) at grain boundary regions (intergranular particles). Amorphous films were found both at Si3N4 grain boundaries and at phase boundaries between Si3N4 and SiC. The Si3N4 grain boundary film thickness varied from 1 to 2. 5 nm. Two kinds of embedded SiC particles were observed: type A has a special orientation with respect to the matrix, and type B possesses a random orientation with respect to the matrix. The surfaces of type B particles are completely covered by an amorphous phase. The existence of the amorphous film between the matrix and the particles of type A depends on the lattice mismatch across the interface. The mechanisms of nucleation and growth of Ω‐Si3N4 grains are discussed on the basis of these experimental results.