Published online by Cambridge University Press: 15 February 2011
The present research was carried out to study the cryogenic synthesis NiAl from elemental powders with the view of forming particle dispersed NiAl. It was found that nanocrystalline NiAl with a crystallite size in the range 5nm to 10nm is produced during cryomilling. Additionally, the nanocrystalline NiAl maintains the fine crystallite size when annealed at high temperatures. It is thought that the resistance of the microstructure to coarsening is due to the presence of nano-scale particles of AIN formed by reaction between milling medium, liquid nitrogen, and aluminum. The transformation of Ni and Al to ordered NiAl was studied using x-ray diffraction. This showed that cryomilling not only produces a solid solution but also can induce in-situ ordering of stoichiometric NiAl. The B2 NiAl structure forms during milling after the elemental powder blend is cryomilled for about 40 hours. It also forms when the “mechanical” solid solution is annealed at room temperature for about twelve hours.