Computer simulation of grain growth-V. Abnormal grain growth

Monte Carlo computer simulation techniques have been utilized to investigate abnormal grain growth in a two dimensional matrix. The growth of abnormally large grains is modelled under two conditions: (a) where the driving force is provided solely by curvature and (b) where the driving force is provided by the difference in the gas-metal surface energy between grains of different crystallographic orientation. For curvature driven growth three cases are considered: (a) the growth of abnormally large grains in microstructures without grain growth restraints, (b) the growth of abnormally large grains in microstructures with particle dispersions, and (c) grain growth in a particle pinned microstructure in which a sudden decrease in the number of particles occurs. In all these cases, the initiation of abnormal grain growth/secondary recrystallization is not found to occur. In systems free from grain growth restraints the normal grain size distribution is very robust and strongly resistant to perturbations. For systems which contain particle dispersions strong pinning of the grain boundaries is always observed. However, when a preferred surface energy orientation is introduced, abnormal grain growth/secondary recrystallization does take place. The microstructural evolution observed during secondary recrystallization is in good correspondence with experiment. The area fraction of secondary grains exhibits sigmoidal behavior as a function of time, and is characterized by an Avrami exponent of 1.8 ± 0.3 when fit to a modified Avrami equation.