Study of nanocrystalline nial alloys prepared by mechanical alloying

Nanostructured powders of Ni-20wt%Al and Ni-50wt%Al were prepared, by mechanical alloying under an argon atmosphere, from elemental Ni and Al powders using a planetary ball mill (type Fritsch P7) for different times (0.5-24h).). Microstructural and structural features of the final products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results of the XRD shows the formation of the B2 (Ni Al) phase after 2 hours of milling for both systems. Also detected was the Ni3Al phase in Ni 80Al20 after 4 hours. Crystallite size refinement of the final product occurred down to nanometer scales when the milling time increased, and attained 17 nm in the Ni50Al50 system and 20 nm in the other system, at 24 hours. This decrease in crystallite size is accompanied by an increase in the interval level strain. The kinetics of Al dissolution during the milling process of Ni50Al50 system can be described by two regimes, characterised by different values of Avrami parameters which are calculated by using the Johnson- Mehl-Avrami formalism. © (2012) Trans Tech Publications, Switzerland.