Determination of nucleation and growth modes from evaluation of transformed fraction in solid-state transformation

On the basis of ail analytical transformation model, the transformed fraction has been evaluated for isothermal and isochronal solid-state transformations. From the evolution of Avrami exponent n with annealing temperature T and the evolution of effective activation energy Q with transformed fraction f, the prevailing modes Of nucleation and growth in the isothermal transformation can be determined. As for the isochronal transformation, however, a conversion of the experimentally obtained continuous-heating-transformation (CHT) diagram to the temperature-time-transformation (TTT) diagram should also be performed. Because the modes of nucleation and growth remain unchanged upon CHT-TTT conversion, the prevailing modes of nucleation and growth in the isochronal transformation can be determined. Using numerical calculations, the above evaluation has been tested. Finally, application in the crystallization kinetics of amorphous Pd-Ni-P-Cu and Mg-Cu-Y as measured by differential scanning calorimetry was described. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.