Thermodynamic calculations of Si-C-O fiber stability in ceramic matrix composites

Thermochemical fiber degradation reactions of multiphase Si-C-O fibers in inert (Ar) and oxidic (air) atmosphere as well as single-phase C and SiC fibers in various carbide, nitride and oxide matrices were calculated in the temperature range 1000-2000°C. The calculations indicate a greater stability of the single-phase SiC as compared to the C fiber in all matrices. The C fiber is fairly stable in AlN and Al2O3 matrix. The silicon carbide fiber is stable in AlN and Si3N4 as well as in Al2O3 and SiO2. Above critical temperatures metal carbides are formed at the fiber-matrix interface. An attempt was made to define boundary conditions for the fabrication of fiber-reinforced ceramic matrix composites.