窒化けい素セラミックスの微細構造と疲労特性の関係

概要

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Microstructures of seven kinds of silicon nitride ceramics were quantified by electron cyclotron resonance plasma etching and sequential image analysis. And the correlations between microstructure and fracture toughness, intrinsic bending strength or cyclic fatigue crack growth exponent were estimated by using multiple regression analysis.The characterized microstructure parameters, composed of the mode and distribution of grain size, the fraction of needle-like grains and the amount of additives, were correlated to the experimental mechanical properties with high correlation coefficients. For improving the fracture toughness, intrinsic bending strength and cyclic fatigue crack growth exponent of silicon nitride ceramics at the same time, it may be effective to increase the needle-like grains, according to the weight factors of microstructure constituents.Fatigue crack growth passages in the materials with highest and lowest fatigue crack growth exponents were analyzed. As a result, in the material with a high exponent, crack arrest and bridging were more often caused by the intergranular fracture of needle-like grains. A larger amount of additives and a broader distribution of grain size make crack arrest and bridging tend to occur more often.