PROCESSING AND MECHANICAL-PROPERTIES OF AL2O3 FIBER-REINFORCED NIAL COMPOSITES

The mechanical properties of NiAl-matrix composites reinforced with 12 5-mu m diameter single-crystal Al2O3 (sapphire) fibers have been exami ned over the temperature range of 300 to 1200 K. Composites were fabri cated with either a strong or weak fiber-matrix interfacial bond stren gth. During fabrication, a fiber-matrix interaction occurred such that fibers extracted from the NiAl matrix were fragmented and significant ly weaker than the as-received fibers. Tensile results of the weakly b onded composite demonstrated that the composite stiffness was greater than the monolithic at both 300 and 1200 K in spite of the weak bond. Room-temperature strengths of the composite were greater than that of the monolithic but below rule-of-mixture predictions (even when the de graded fiber strengths were accounted for). At 1200 K, the ultimate st rength of the composite was inferior to that of the monolithic primari ly because of the poor fiber properties. No tensile data was obtained on the strongly bonded material because of the occurrence of matrix cr acking during fabrication. Primarily because of the fiber strength los s, sapphire-NiAl composite mechanical properties are inferior to conve ntional high-temperature materials such as superalloys and are current ly unsuitable for structural applications.