Sub-grain boundary formation in Si3N4 based ceramics

Present paper deals with the residual stresses localized within the grains of silicon nitride based composites. The stresses are a consequence of processing, grain growth and/or a presence of other phases with different thermal expansion. These stress fields locally weaken the grains and thus can be considered as the sub-grain boundaries which definitely influence the composite. This kind of sub-grain boundaries and their possible effect on the room temperature mechanical properties are presented for two materials, beta-Si3N4 whisker reinforced Si3N4 ceramics and SiC/Si3N4 nano-micro composites