FLUOROMICA COATED NICALON FIBER-REINFORCED GLASS-CERAMIC COMPOSITES

High temperature structural behavior was demonstrated in Nicalon fiber reinforced glass-ceramic matrix composites by means of a functional weak fluoromica interface. Sheet silicate interfaces were evaluated from both the mica matrix and sol-gel derived fluoromica fiber coatings in a calcium aluminosilicate (CAS) matrix. The Nicalon fiber reinforced mica matrix composites were found to fail early in shear owing to the cleavage dominated mica matrix, whereas the potassium-phlogopite mica coated composite provided much higher strength with tensile failure mode. The oxidative stability inherent in the fluoromica interface led to the enhanced oxidation enbrittlement resistance of the composites at high temperatures in an aerobic environment, in contrast to the severe embrittlement seen in uncoated Nicalon fiber reinforced composites with the in situ carbon-rich interface. Microstructural and mechanical studies of potassium-phlogopite coated N/CAS II composites are presented, along with the synthesis and characterization of potassium-phlogopite precursor sol.