Observation of Fracture Source in High Strength Silicon Nitride-Based Ceramics

In order to investigate whether the fracture of high strength Si3N4-based ceramics does occur or not from one or one set of observable microstructural defect acting as the fracture source, the fracture surfaces of the fragments for each 18 test piece of four kinds of high strength Si3N4-based ceramics supplied by three manufacturers were precisely observed by using SEM.The results obtained were as follows. (1) It was confirmed for all kinds of specimens that the fracture always occurred from one or one set of observable microstructural defect as the fracture source, even when the strength was very close to the attainable flexural strength. (2) The above results indicate that the average flexural strength can be further increased even for high strength Si3N4-based ceramics by decreasing the amount and size of the microstructural defects and that the effects of variables on the strength should be analyzed by taking into consideration of the microstructural defect which acted as the fracture source.