Study on Strength and Fatigue of Ceramic Materials

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In order to clarity the behavior of grain boundary, which controls the strength and fatigue of ceramic polycrystals, the properties of amorphous materials having similar structure to that of grain boundary were investigated. The following results were obtained: (1) The glass-forming regions were clarified for the systems containing rare-earth oxides being used for sintering aid, and furthermore their deformation and crystalline temperatures were determined. (2) Viscosity, density, hardness and thermal expansivity were determined for the amorphous materials in the <Si_3> <N-4> Si <O_2> -CaO system. (3) The amorphous materials obtained by RF-sputtering for the systems Ti <O_2> -Si <O_2> , Zr <O_2> -Si <O_2> and <A1_2> <O_3> -Si <O_2> were examined for their structure and properties, and some abnormal coordination states of cations were found. (4) The experimental ways to determine the chemical bond strength were established for multi-component glasses and the results were compared with the theoretical ones. (5) The effects of chemical composition, coordination number, crystallization, plastic deformation and inhomogeneity on elastic moduli and fracture toughness were examined based on the experimental data for glass and a possibility to increase the toughness was discussed.