Microstructural Evolution in Annealed and Crept Silicon Nitride

The microstructure of a commercial sintered silicon nitride has been examined in the as‐sintered condition, after annealing to a stable microstructure in either air or argon, and after creep deformation. Both as‐sintered material and material annealed to a stable microstructure were crept. Extensive analytical electron microscopy has been used to determine the composition of the intergranular material (amorphous and crystalline). The as‐sintered material contains an amorphous intergranular phase which partially devitrifies upon exposure to high temperatures. The residual intergranular glass is homogeneous throughout the samples (even though different crystalline products form near the surface and in the center of samples annealed in air) and stable. Creep deformation does not affect the microstructural evolution. It is, however, responsible for internal strain and some cavitation in the material.