Silicon Nitride Based Ceramic Nanocomposites

Nanocomposites (Si 3 N 4 /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: Si 3 N 4 matrix grains (0.5 μΩ), nanosized SiC particles (<100 nm) embedded in the Si 3 N 4 , and large SiC particles (100–200 nm) at grain boundary regions (intergranular particles). Amorphous films were found both at Si 3 N 4 grain boundaries and at phase boundaries between Si 3 N 4 and SiC. The Si 3 N 4 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‐Si 3 N 4 grains are discussed on the basis of these experimental results.