Abstract
Alumina–NiAl composites were prepared by powder metallurgy processing for the evaluation of mechanical properties as a function of composite composition. Fine alumina powder and coarse angular NiAl particles were attrition milled for different time periods, using zirconia grinding media, resulting in the NiAl particles being squeezed into elongated flakes. Dense composites were prepared by hot pressing in graphite dies at 1450°C and samples prepared for microstructure and properties characterisation. Increase in milling time was found to increase the aspect ratio of the NiAl flakes which aligned perpendicular to the hot pressing direction during fabrication. The strength and toughness of the composites were found to be higher than predicted by the rule of mixtures and this is ascribed both to the bridging effect of NiAl flakes between crack surfaces, which is enhanced by the increased aspect ratio from increased milling time, and microstructural refinement from grain growth inhibition.
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