KINETICS OF REORDERING OF NI3AL DISORDERED BY BALL-MILLING

A systematic study of the kinetics of the reordering process, followed by X-ray diffraction and differential scanning calorimetry, of a Ni, Al based alloy, previously disordered by high energy ball-milling, is reported. X-ray diffraction analysis of isothermally annealed samples gives apparent activation energies of 1.57 +/- 0.20 eV for reordering and 1.61 +/- 0.07 eV for ordered domain growth. Good agreement is found between these values and that obtained from the calorimetric analysis of the continuous heating transformation, which gives a value for the apparent activation energy of 1.64 +/- 0.21 eV. However, in order to correctly reproduce the calorimetric results obtained upon isothermal annealing, an increasing value for the apparent activation energy of the process is needed. As the experimental results suggest that point defect diffusion has an active role in the reordering process, a vacancy trapping mechanism via impurity is put forward to account for the slowing down of the kinetics of reordering.