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

The mechanical properties of NiAl-matrix composites reinforced with 125-mu m diameter single-crystal Al2O3 (sapphire) fibers have been examined over the temperature range of 300 to 1200 K. Composites were fabricated with either a strong or weak fiber-matrix interfacial bond strength. During fabrication, a fiber-matrix interaction occurred such that fibers extracted from the NiAl matrix were fragmented and significantly weaker than the as-received fibers. Tensile results of the weakly bonded 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 degraded fiber strengths were accounted for). At 1200 K, the ultimate strength of the composite was inferior to that of the monolithic primarily because of the poor fiber properties. No tensile data was obtained on the strongly bonded material because of the occurrence of matrix cracking during fabrication. Primarily because of the fiber strength loss, sapphire-NiAl composite mechanical properties are inferior to conventional high-temperature materials such as superalloys and are currently unsuitable for structural applications.