OXIDATION OF AL2O3 CONTINUOUS FIBER-REINFORCED NIAL COMPOSITES

The 1200-degrees-C and 1300-degrees-C isothermal and cyclic oxidation behavior of Al2O3 continuous fiber (Saphikon(TM))-reinforced/NiAl composites were studied Oxidation resulted in formation of Al2O3 external scales in a similar manner as scales formed on monolithic NiAl. The isothermal oxidation of an Al2O3/NiAl composite resulted in oxidation of the matrix along the fiber/matrix interface near the fiber ends. This oxide acted as a wedge between the fiber and matrix, and, under cyclic oxidation conditions, led to further oxidation along the fiber lengths and eventual cracking of the composite. The oxidation behavior or composites in which the Al2O3 fibers were sputter coated with nickel prior to processing was much more severe. This was attributed to open channels around the fibers which formed during processing most likely as a result of the diffusion of the nickel coating into the matrix.