Modelling recrystallisation

Abstract

The Johnson–Mehl–Avrami–Kolmogorov (JMAK) theory for recrystallisation has been modified by using an analytical approach and three dimensional computer simulations. A non-constant growth rate, the result of either spatial variations in the net driving force for the recrystallisation reaction, or simultaneous recovery during the reaction, has been considered. Either may account for considerable negative deviations from classical JMAK kinetics. The effect of recovery on transformation kinetics in the case of site saturated nucleation is analysed in detail. An inhomogeneous distribution of nucleation sites may also have a significant effect on the kinetics; leading to non-constant Avrami exponents usually much lower than the classical values of 3 and 4for three dimensional homogeneous site saturation and Johnson-Mehl nucleation kinetics, respectively. It is suggested that the near log-normal size distributions of grain section areas which are commonly observed experimentally may reflect a non-random distribution of nucleation sites. The modelling results are discussed in terms of experimental observations. MST/1294