Mechanical properties of NiAl–AlN–Al2O3 composites

The mechanical properties of NiAl-based composites containing a dispersion of AlN particles and Al2O3 fibers were studied. NiAl matrix powder containing a dispersion of about 5 vol.% AlN was synthesized by mechanical alloying (MA) of elemental nickel and aluminum under a nitrogen gas atmosphere. Nextel 610 short fibers were used as the second reinforcement in the composite. Composites containing 5, 15 and 30 vol.% of the Al2O3 fibers in addition to the AlN dispersion particles were fabricated by hot pressing a dry blend of the MA NiAl powder and the fibers. The as-fabricated microstructures revealed that the matrix is fully dense and bonded well with the randomly distributed Al2O3 fibers. Neither chemical reaction nor cracks were observed at the fiber/matrix interface. Compressive behavior of the composites and a monolithic counterpart was studied at 1300 K and strain rates between 8.5×10−4 and 2.8×10−6 s−1. The 0.2% yield stress of the composites increases with fiber volume fraction at all strain rates. The strain rate–flow stress behavior at 1300 K indicates that the strength of NiAl–5%AlN–30%Al2O3 approaches that of NASAIR 100, a first generation Ni-base single crystal superalloy.