Long term stability and mechanical properties of Al2O3–NiAl composites reinforced with partially fragmented long fibers

Long fiber reinforced NiAl composites, fabricated by high temperature processing, are designed for long term thermal exposure during service. This treatment causes partial fragmentation of the long fibers, which degrades the mechanical performance of the composite. We investigated the mechanical properties of Al2O3–NiAl long fiber composites, fabricated by hot pressing and exposed to 2000 h annealing at 700 °C and 1100 °C. The composites showed basically good thermal stability during annealing except for grain coarsening of NiAl. Owing to fiber fragmentation during cooling after composite fabrication, the mechanical performance of the composites is determined by the load partitioning in a mixture of long and broken fibers. We propose a method to calculate the strength of such composites, based on microstructural information and composite fracture mechanisms. The theoretical predictions show good agreement with experimental results.