Microstructural evaluation of deformation mechanisms in silicon nitride ceramics

Changes of phase composition and chemistry during deformation testing in compression of silicon nitride were investigated. The specimens were rapidly consolidated to maintain the initial alpha phase. In initial compressive deformation testing, 70% true strain was achieved at strain rates of 5 × 10-6 s-1. Phase transformation was noted to occur during compressive deformation testing over the range of temperatures investigated. Grain boundary chemistry was determined with a JEOL 200 CX Analytical Electron Microscope (AEM) and an 8000 KEVEX System. The phase compositions of individual silicon nitride grains were determined by indexing of electron beam diffraction patterns.