1988 年 37 巻 421 号 p. 1197-1203
Areal inspections by EPMA (electron probe micro-analyser) were made to identify the distributions of impurity elements existing at fracture origins on the ruptured surface of silicon nitride specimens which were tested under tensile load at room temperature. Parallel observations by SEM (scanning electron microscope) were also made to detect the inherent defects at fracture origins. It was found that even if no geometrical defect like a void was observed by SEM at fracture origins, dense segregation of impurity elements such as Fe, Ti and C was found at corresponding sites by EPMA. Therefore, both of the geometrical defects and segregation type defects must equally be treated in the analysis of fracture mechanism. This point was further discussed in this study, and it was concluded that the stress intensity values calculated from the size of both types of defects and the applied load were well correlated with the fracture toughness KIC of this material.