Fabrication, Structure and Consolidation of NiAl-Al$\text{}_{2}$O$\text{}_{3}$ Mechanically Alloyed Nanocomposite Powders

Reactive milling of NiO + Al powder mixture resulted in the formation of NiAl-Al$\text{}_{2}$O$\text{}_{3}$ nanocomposite powders, with a crystallite size of about 20 nm. The Hall-Williamson analysis revealed that NiAl showed an orientation dependent crystallite size after short processing time and orientation dependent internal strain after long milling time. Both anisotropies were removed by heating the powders in the differential scanning calorimetry. Calorimetric studies showed one exothermic effect attributed to the reduction reaction of NiO and endothermic one associated with melting of Al. Two methods were applied for powders compaction: resistance sintering and pulse electric discharge. In both cases the densities of about 90% of the theoretical value were achieved. A significant increase in average NiAl crystallites size in compacted samples was observed, up to several hundreds of nanometers.