FABRICATION, MICROSTRUCTURE, AND MECHANICAL-PROPERTIES OF TAC PARTICULATE AND SIC FIBER-REINFORCED LITHIA-ALUMINA-SILICA COMPOSITES

Additions of 0 to 9 mol% Ta2O5 to a lithia-alumina-silica glass-cerami c matrix Nicalon SiC-reinforced composite increased the elastic modulu s and ultimate strength of the composite. The additive fostered sphere ulitic growth of beta-eucriptite solid solution crystals which concent rated Ta2O5 at sphereulite boundaries and adjacent to the fiber-matrix carbon-rich interphases. These regions reacted with the interphases a s well as soluble carbon monoxide gas to convert them to TaC. The form er reaction was shown to be thermodynamically favorable above 983 degr ees C, while the latter was favorable above 1249 degrees C. The improv ement in mechanical properties was attributed to TaC particulate reinf orcement, and suggests a simple glass-ceramic route to the fabrication of particulate-reinforced ceramic matrix composites.