Static recrystallization kinetics with homogeneous and heterogeneous nucleation using a cellular automata model

The kinetics of homogeneous and heterogeneous static recrystallization in a single-phase material were analyzed using two-dimensional (2-D) and three-dimensional (3-D) cellular automata (CA). A CA model was developed, which was then validated using the theory based on relationships developed by Johnson and Mehl, Avrami, and Kolmogorov (JMAK) for homogeneous site-saturated and constant-rate nucleation. The model was then modified for heterogeneous nucleation at grain boundaries, with either a fixed number of nuclei or a constant rate of nucleation. The fraction of boundary sites nucleated, for the case of fixed nucleation, varied from 0.006 to 0.28, resulting in Avrami exponents (k) ranging from 1.8 to 1.1 (site saturation). Site saturation with fixed nucleation produced a lamellar microstructure. The parameters of q and m, from Vandermeer’s microstructural path method, were calculated and compared with theoretical values. Constant-rate nucleation at grain boundaries between newly recrystallized grains and the unrecrystallized matrix resulted in k values of ≈1. Simulated microstructures revealed that with a low nucleation rate, recrystallized grains formed in clusters, while a high nucleation rate resulted in a necklace microstructure, with kinetics similar to those observed in dynamic recrystallization (k=1.4).