AL2O3 FIBER STRENGTH DEGRADATION IN METAL AND INTERMETALLIC MATRIX COMPOSITES

The mechanisms for fiber damage in single crystal Al2O3 fiber-reinforc ed composites were investigated. Both fiber fragmentation and fiber st rength degradation were observed in composites with a variety of matri x compositions. Four mechanisms that may be contributing to the fiber strength loss have been proposed and include matrix reaction, reaction with binders, residual stress-induced damage, and pressure from hot p ressing. The effect of matrix reaction was separated from the other th ree effects by sputter-coating the matrices on cleaned fibers and anne aling with a temperature profile that simulates processing conditions. These experiments revealed that Y and Cr in FeCrAlY base alloys and Z r in NiAl alloys reacted with the fiber, and grooves and adherent part icles were formed on the fiber surface which were responsible for the strength loss. The effects of the matrix reaction appeared to dominate over the other possible mechanisms, although evidence for reaction wi th binders was also found. Ridges on the fiber surface, which reflecte d the grain boundaries of the matrix, were also observed. In order for single-crystal Al2O3 to be used as a fiber in MMC's and IMC's, a matr ix or protective coating which minimizes matrix reaction during proces sing will be necessary. Of the matrices investigated, the Thermo-span( TM) alloy was the least damaging to fiber properties.