An X-Ray Diffraction Study of Mechanical Activation-Induced Structural Changes in Ni + Al Mixtures Containing Nickel Powders Prepared by Different Techniques

Abstract—

Mechanically activated Ni + Al mixtures containing two types of nickel powder, PNK (carbonyl nickel) and PNE-1 (electrolytic nickel), have been characterized by X-ray diffraction. The behavior of structural parameters of the mixtures containing both nickel powders has been studied as a function of milling time. During milling, the internal stress of the nickel and aluminum in the mixture containing the PNK nickel powder reaches a higher level in comparison with the PNE-1 powder. Moreover, in the case of the PNK powder, synthesis directly in the grinding vial of the mill requires a longer milling time in comparison with the PNE-1 powder (11 and 7 min, respectively). Milling for a time shorter than the critical one increases the density of structural defects in both mixture components (as evidenced by an increase in the full width at half maximum of X-ray diffraction peaks and a reduction in their intensity). Mechanical activation produces different structural changes in the nickel and aluminum: the maximum internal stress in the nickel exceeds that in the aluminum, but the aluminum is comminuted to a higher degree (its crystallite size decreases to a lower level).