INTERFACIAL PHENOMENOLOGY OF SIC FIBER REINFORCED LI2O.AL2O3.6SIO2 GLASS-CERAMIC COMPOSITES

The microstructures of SiC fibre-reinforced Li2O.Al2O3.6SiO2 glass-ceramic composites with Ta2O5, Nb2O5, TiO2 and ZrO2 dopants were investigated. An amorphous carbon-rich layer, from 100-170 nm thick, was observed in the interfacial region between fibre and matrix. A second interfacial layer of TaC, NbC, or TiC precipitates, appeared adjacent to the C-rich layer. Low bond strength between these two interfacial layers resulted in low interfacial shear strength, and this in turn led to an increase in toughness of the composites containing 4 mol% Ta2O5 or Nb2O5 dopant. 2 mol% Ta2O5 dopant in this composite acted as a nucleating agent for the matrix but was not adequate to form an appreciable volume of TaC particles in the interfacial region, hence a flexural strength decrease was observed. The composite containing TiO2 dopant exhibited low flexural strength and fracture toughness resulting from the formation of a TiC layer which had a larger coherent bond strength with the interfacial C-rich layer, and attacked the structural integrity of the fibres.