MICROSTRUCTURE AND MICRO-INDENTATION FRACTURE OF SIC-WHISKER-REINFORCED SI3N4 COMPOSITE STUDIED BY HIGH-RESOLUTION ELECTRON-MICROSCOPY

Microstructure and fracture behavior of a SiC-whisker-reinforced Si3N4 composite have been investigated by transmission (TEM) and high-resolution electron microscopy (HREM) and micro-indentation fracture (MIF) technique. SiC whiskers (SiC(w)) are homogeneously dispersed in the Si3N4 matrix. Most of the SiC(w) have a beta-type cubic structure with many twins and stacking faults. Amorphous layers of about 1 nm in thickness are observed at Si3N4 grain boundaries and Si3N4/SiC(w) interfaces. Cracks mainly propagate along the Si3N4 grain boundaries and Si3N4/SiC(w) interfaces in the indentation made at room temperature and 1200-degrees-C. Fracture toughening effects are due to multi-mechanism of crack deflection, bridging and microcracking.