Additivity rule, isothermal and non-isothermal transformations on the basis of an analytical transformation model

Abstract

In the present work, the “additivity rule” was proved to be compatible with an analytical transformation model assuming mixed nucleation (with site saturation and continuous nucleation as two extremes), for some specified conditions. Combining the analytical model with numerical calculations, it is practicable to allow a conversion of continuous heating or cooling transformation (CHT or CCT) data into isothermal transformation data (TTT), and also a conversion of TTT data into CHT or CCT data, under a restrictive assumption of constant cooling or heating rate. From a comparative study between TTT and CHT data, the effective activation energy was found to increase and decrease, respectively, as compared with that before the CHT–TTT and TTT–CHT conversions; the growth exponent was proved to hold almost invariably, independent of the conversions. Real applications in the crystallization of amorphous Mg–Ni alloy and in the gamma–alpha massive transformation in Fe–Mn alloy show that the above conclusions are reasonable.