Advances in permanent magnets

NiAl and Ni3Al were atomised in a sonic nitrogen gas atomiser. The frequency of dendritic or equiaxed morphologies in the powders depends on powder size for NiAl, while it is fairly independent of powder size for Ni3Al. The cooling rates were computed by means of a finite difference code as a function of powder size and related to grain size or secondary dendrite arm spacing for NiAl and Ni3Al respectively. Nitrogen uptake was determined by a Leco analyser and was found to depend on powder size.