A systematic study of the kinetics of the re-ordering process, followed by X-ray diffraction and differential scanning calorimetry, of a Ni3Al based alloy, previously disordered by high energy ball-milling, was reported. X-ray diffraction analysis of isothermally annealed samples gave apparent activation energies of 1.57eV for reordering and 1.61eV for ordered domain growth. Good agreement was 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 1.64eV. However, in order to correctly reproduce the calorimetric results upon isothermal annealing, an increasing value for the activation energy of the process was needed. As the experimental results suggest that point defect diffusion has an active role in the reordering process, a vacancy trapping mechanism via impurity was put forward to account for the slowing down of the kinetics of reordering.

Kinetics of Reordering of Ni3Al Disordered by Ball-Milling. Baró, M.D., Suriñach, S., Malagelada, J., Clavaguera-Mora, M.T., Gialanella, S., Cahn, R.W.: Acta Metallurgica et Materialia, 1993, 41[4], 1065-73

Table 34

Calculated defect formation energies

for stoichiometric Ni3Al at 1400K