CALORIMETRIC ANALYSES OF MECHANICALLY ALLOYED NI3AL-BASED POWDERS

In this paper, the progress on disordering and the study of the reorde ring kinetics of nanocrystalline Ni,Al-based powders prepared by ball- milling were followed by differential scanning calorimetry. A broad ex othermic transformation occurs on heating the nanocrystalline Ni3Al-ba sed powders. The stored energy of cold work has been evaluated by meas uring the enthalpy release during heating. The values obtained far exc eed the energies achieved by conventional deformation processes. The s pecific heat increases by more than 5%, indicating changes in vibratio nal and configurational part of the entropy. The calorimetric analysis of the continuous heating transformation, gives a value for the appar ent activation energy of 1.64 +/- 0.07 eV, which is very close to the reported values of the activation energies for vacancy migration in th ese alloys. However, in order to correctly reproduce the calorimetric results obtained upon isothermal annealing, an increasing value for th e apparent activation energy of the process is needed. The possible me chanisms involved in the reordering process are discussed.