Basic Research on the Fracture Phenomena of Ceramics with Particle Dispersion

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The present study was undertaken to obtain a basic information on the effect of various microstructural variables on the toughening and slow crack growth mechanisms in ceramics containing second-phase dispersions. Model two-phase composites were used for study.Glass matrix/alumina particle and glass matrix/magnesia particle composites where thermal expansion coefficient of dispersed particles is greater than that of a matrix were prepared by hotpressing and toughening mechanisms in these composites were investigated. In both composite systems, fracture toughness were found to increase with increasing second-phase particles, but toughness behavior depends strongly on particle size, particle morphology and degree of thermal expansion mismatch between constituent phases. During fracture process of the composites studied, crack bowing and crack deflection mechanisms were considered to act as major toughening mechanisms. In addition, for the composite systems where a condition for spontaneo … More us microcrak formation due to thermal expansion mismatch is satisfied, microcracking mechanism may contribute to toughness increase.Glass matrix/alumina particle and glass matrix/silica particle composites where thermal expansion coefficient of dispersed particles is smaller than that of a matrix were investigated with special reference to microcrack toughening. Toughness behavior of glass-alumina composites were compared with that of glass-silica composites in which only thermal expansion mismatch exists. A basic information on the condition for the occurrence of microcracking mechanism during fracture was obtained.The slow crack growth characteristics of indentation-induced microcracks in phase-separated lead borate glasses with particulate microstructure were investigated. Vickers indentation were made on the polished surface of the specimens and the extension of induced crak under residual stress field was monitored over a time after unloading. Experimental results were interpreted in terms of microstructural factors and crack-particle interaction mechanisms during slow growth wtage under moist environment were clarified. Less