Two models of solid–solid transformation kinetics in the CuAu intermetallic compound

A simple model of the kinetics of order–disorder and order–order transformations in the stoichiometric CuAu compound is presented. The model describes the evolution of the Gibbs energy of stable and metastable states of two ordered (CuAu(I), CuAu(II)) and one disordered (CuAu(D)) phase. The simultaneous kinetics of all three phases is interpreted as a result of six competitive transformation processes. The model is employed for a semi-quantitative description of the TTT curves, for differential scanning calorimetry modelling and also for an interpretation of the so-called retro-effect in CuAu. The proposed phenomenological description of kinetic processes in CuAu is compared with the classical concept of the theory of nucleation and growth kinetics. Both theories are discussed in terms of real processes, accompanying the transformations in CuAu (elastic effects, anti-phase boundaries, twinning, hysteresis effects, spinodal ordering).