Transmission Electron Microscope Observation of Creep-Deformed Al_2O_3; SiC and Si_3N_4 Ceramics

摘要

Microstrural observation using transmission electron microscope were conducted on creep-deformed SiC, Al_2O_3 and Si_3N_4 ceramics in order to analyze microscopic deformation mechanism in these ceramics directly. thin foild were prepared from the tensile surface of the four-point bending bars after creep test at various conditions. In SiC ceramics crep at 1250degC, very sharp microcracks propagated relatively straight andn transgranularly. Microcracks also branched and some of them extended along grain boundary. In SiC crept at 1480degC, grain boundary cavities and dislocations were also obseved. In Si_3N_4 crept at around 1200degC, cavities along grain boundary were frequently observed. In Si_3N_4 crept at around 1200degC, cavities along grain boundary were frequently observed. Dislocations were sometimes observed. No transgranular cracks were happened. In Al_2O_3 ceramics crept at 1000degC, sharp microcracks ran throgh both grain boundary and inside grains with small number of very tiny grain boundary cavities. Grain boundary glassy phase was partly crystallized. Based on the observed microstructure, creep mechanisms of these ceramics were discussed in relation with creep ductility.