Simulation Of Grain Evolution With Cellular Automata

The process of normal grain growth, coarsening for both single and binary phase, as well as dynamic recrystallization, studied using Cellular Automata (CA) approach in this paper. And grain growth for single phase and dynamic recrystallization under the condition of nonhomogeneous temperature field were also investigated preliminarily.The model simulating the process of normal grain growth using modified CA model was set up by introducing the lowest energy principle. The simulation results indicate that a lot of grains exhibit 5, 6, or 7 latus, in which hexagonal grains have a largest amount; equiaxed grains are favorited with triple-point junctions of about 120 degree, which is the same as that of realitic circumstances; two basic topological transfers were found in simulating process. The grains grow through phagocytizing the smaller grains in the size or in the latus phagotrophy by larger grains. And normal grain growth exponent of 0.472 is obtained, which is much closed to theoretical value of 0.5. The research of influence of temperature on grain growth indicates that higher temperature accelerates grain growth, but has a little influence on the growth exponent.The process of grain growth in the annealing process of TA15 alloy at 1050℃was simulated by the normal grain growth model. Growth exponent getted from the simulation is 0.481, very close to the experiment value of 0.4876. The variation of the grain's mean diameter with the time step from simulation is well in agreement with that of experiment.The normal grain growth model of single phase was applied in the condition the nonhomogeneous temperature by introducing the temperature variable. The rule of normal grain growth in the nonhomogeneous temperature field was studied, and the process of grain's nucleation, growth in different temperature area also was revealed.The model applied in binary phase has been constructed by distinguishing the phase by the date of the orientation of the cell. The simulation result indicates that the grains of each phase impede the growth of other phase grain under the condition of equal initial phase content. If one phase initial content is larger than other phase, the phase with a small amount will block another phase growth; if one phase is much less than another phase, its grain growth will be very difficult.To realize the dynamic recrystallization CA model, the dislocation density, the nucleation, the grain growth and recovery model has been constructed, respectively, by analyzing the variation of dislocation density in the thermal deformation process. The dynamic recrystallization process, as well as micro-structure evolution during dynamic recrystallization process, has been studied. The Avrami curve getted from the simulation agrees well with the kinetics theory of dynamic recrystallization. The influence of strain rate is studied. And the results showed that, under the condition of fixed strain with low value, high strain rate leads to small mean diameter of dynamic recrystallization grains and low DRX percentage, i.e., DRX process is more inadequate.The process of dynamic recrystallization with the nonhomogeneous temperature field is studied preliminarily. The results indicate that the lower temperature area presents earlier nucleation, slower grain growth and finer ultimately R-grain.