MICROSTRUCTURE AND PROPERTIES OF SIC WHISKER REINFORCED CERAMIC COMPOSITES

Microstructures of SiC whisker reinforced alumina and tetragonal zirconia polycrystals (TZP) were investigated using analytical electron microscopy. In the Al2O3-SiC system, amorphous phases between the whisker and matrix were observed; these amorphous phases were virtually eliminated when the whiskers were leached with HF acid before being incorporated into the matrix. In the TZP/SiC system, reaction between the whisker and matrix had taken place during fabrication and resulted in the formation of a glassy phase. This reaction appeared to be associated with the presence of SiO2 impurity present in the TZP matrix. Mechanical properties of the composites were measured both at ambient and elevated temperatures and fracture surfaces were examined. The results indicated that fracture of the composites was sensitively influenced by the whisker-matrix interface. The presence of amorphous interfacial phases was detrimental to the properties of the composites and caused a reduction in fracture energy. High temperature tests showed that the TZP composite had a structural transition with extensive cracking occurring at 1000-degrees-C, whilst the alumina composites retained their properties up to 1200-degrees-C, whereupon they deteriorated rapidly.