Transmission Electron Microscope Observation of Creep-Deformed Al_2O_3, SiC and Si_2N_4 Ceramics

摘要

Microstructural observation using transmissionelectron microscope were conducted on creep-deformed SiC,Al_2O_3 and Si_3N_4 ceramics in order to analyze microscopicdeformation mechanism in these ceramics directly. Thin foilswere prepared from the tensile surface of the four-point bendingbars after creep test at various conditions. In SiC ceramics creptat 1250 deg C, very sharp microcracks propagated relativelystraight and transgranularly. Microcracks also branched andsome of them extended along grain boundary. In SiC crept at1480 deg C, grain boundary cavities and dislocations were alsoobserved. In Si_3N_4 crept at around 1200 deg C, cavities alonggrain boundary were frequently observed. Dislocations weresometimes observed. No transgranular cracks were happened. InAl_2O_3 ceramics crept at 1 000 deg C, sharp microcracks ranthrough both grain boundary and inside grains with smallnumber of very tiny grain boundary cavities. Grain boundaryglassy phase was partly crystallized. Based on the observedmicrostructure, creep mechanisms of these ceramics werediscussed in relation with creep ductility.