Si3N4系セラミックスの微構造と破壊挙動

概要

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Relationship between microstructure and fracture behavior of monolithic Si3N4 and Si3N4/25vol%SiC nanocomposites was investigated. For the Si3N4/25vo1%SiC nanocomposites, the fracture strength was increased by the nano-size SiC dispersion which allowed to control the growth of fine and uniformly elongated Si3N4 grains. Fracture toughness was also improved because of bridging and pull-out of elongated Si3N4 grains. The variation of the fracture toughness value with the indentation load, i.e. crack length, was measured by indentation fracture (IF) method, and this result was compared with that of chevron notched beam (CNB) method. In this experiment, the fracture toughness by IF method exhibited a rising with increasing the crack length. This was interpreted as due to the rising R-curve behavior also observed by the CNB method. Therefore, it is proposed that R-curve behavior can be also estimated by IF method. However, the saturated KR value observed by IF method was within ±15% of measured by CNB method.
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