Calorimetric Analyses of Mechanically Alloyed Ni<inf>3</inf>Al-Based Powders (Overview)

In this paper, the progress on disordering and the study of the reordering kinetics of nanocrystalline Ni3Al-based powders prepared by ball-milling were followed by differential scanning calorimetry. A broad exothermic transformation occurs on heating the nanocrystalline Ni3Al-based powders. The stored energy of cold work has been evaluated by measuring the enthalpy release during heating. The values obtained far exceed the energies achieved by conventional deformation processes. The specific heat increases by more than 5%, indicating changes in vibrational and configurational part of the entropy. The calorimetric analysis of the continuous heating transformation, gives a value for the apparent activation energy of 1.64±0.07 eV, which is very close to the reported values of the activation energies for vacancy migration in these alloys. 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. The possible mechanisms involved in the reordering process are discussed. © 1995, The Japan Institute of Metals. All rights reserved.