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 dev eloped, which was then validated using the theory based on relationshi ps developed by Johnson and Mehl, Avrami, and Kolmogorov (JMAK) for ho mogeneous site-saturated and constant-rate nucleation. The model was t hen modified for heterogeneous nucleation at grain boundaries, with ei ther a fu;ed number of nuclei or a constant rate of nucleation. The fr action of boundary sites nucleated, for the case of fixed nucleation, varied from 0.006 to 0.28, resulting in Avrami exponents (k) ranging f rom 1.8 to 1.1 (site saturation). Site saturation with fu;ed nucleatio n 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 r esulted in k values of approximate to 1. Simulated microstructures rev ealed that with a low nucleation rate, recrystallized grains formed in clusters, while a high nucleation rate resulted in a necklace microst ructure, with kinetics similar to those observed in dynamic recrystall ization (k = 1.4).