Abstract
The effect of microstructure of silicon nitride on dynamic fracture toughness (KId) measured by one-point-bending impact test method was investigated. The specimens were sintered in the temperature range of 1823K to 2073K in N2 atmosphere, followed by hot isostatic pressing (HIPing) . Pressureless sintered (P.L.S.) silicon nitride was increased in density with sintering temperature. HIPed silicon nitride showed almost full density (3.26 X 10-3 kg/m3). In the case of P.L.S. silicon nitride, static fracture toughness (KIc) and dynamic fracture toughness (KId) have tendency to increase with sintering temperature. In HIPed silicon nitride, KIc had tendency to increase slightly with sintering temperature, but Kid was almost constant. Both silicon nitride was observed grain growth with sintering temperature which was observed by electron microscope, but the difference of microstructure between P.L.S. and HIPed silicon nitride was not observed. In the case of HIPed silicon nitride, we thought the following : specimen was broken along the grain boundary under the influence of grain size for static fracture, and specimen was broken abruptly without regard to particle and grain boundary for dynamic fracture.
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