Study On Modeling And Simulation Of Recrystallization Annealing Process For Textural Materials By Monte Carlo Method

With the development of computer simulation technology, the science of material preparation is changing from traditional design to reverse manner, which makes it possible to design its components, microstructure and forming technology based on the properties of material. Forming and heat treatment are important to material's microstructure and properties, the latter of which is of vital importance. Texture, which is the deviation of random orientation distribution, has a significant impact on the material properties and has attracted the wide attention of scholars of materials science. In recent years, the formation and evolution of texture is becoming a hot research topic in material design, especially the simulation of recrystallization annealing of textural materials.Monte Carlo (MC for short) method is a numerical calculation technique based on probability and statistics theories. The MC Potts model can be capable of analyzing complicated microstructure and visualizing the process of the emulation, which is widely used in materials science and lays a good foundation for the simulation of recrystallization annealing of textural material. Therefore, the simulation of recrystallization annealing of textural materials is studied by MC method in order to forecast recrystallization structure and texture evolution, optimize annealing process, and research the corresponding theories and technologies, which is of great theoretical and practical value.Firstly, several key technologies of simulation were developed for modeling and analyzing the simulated results in this paper. These included: 1) A new method was proposed to calculate grain size; 2) Two methods were presented to calculate grain side number and the corresponding applications were introduced; 3) A new three-parameter nonlinear fitting method was proposed, which improves the fitting precision of grain growth exponent; 4) A modified Voronoi model was established to generate the deformed microstructure which depends on the mean strain and the grain size distribution.Secondly, the effects of some parameters of normal grain growth (NGG) MC model, i.e. the lattice types, the method of selecting lattice sites, the methods of selecting new orientation and the neighbors selection for energy calculation, on the simulation results of grain growth were comprehensively investigated. An optimal model with appropriate parameters including triangular lattice, the attempted site selected randomly, the new orientation selected from neighboring ones randomly and the first and second nearest neighbors for energy calculations was obtained by comparing the grain growth exponents and the simulating efficiencies.Thirdly, to extend the modeling dimension, a 3D NGG-MC model with triangular lattice was presented, which was compared with cubic lattice. The distributions of grain size and grain plane for the both models are consistent with theoretical analysis, and the grain growth exponent is much more close to the theoretical value when the model is with triangular lattice and energy calculations considering a wider neighboring sites range.Fourthly, on the basis of 2D NGG optimizing model, a new grain growth MC model of textural material was established. In the new model, the grain orientations are expressed by Euler angle, which makes the grain orientation and the misorientation has actual meaning. The texture in the initial structure can be set by experimental data to simulate the effects of texture on grain growth. The new model can be used to simulate both the NGG and the abnormal grain growth of textural material. Abnormal grain growth of the initial microstructure with only exist cube texture and the grain size distribution followed lognormal function was simulated. The results showed that the possibility of abnormal growth and the average grain size increase with broadening of the half-width of texture; but the influence of the volume fraction is relatively small; only if the half-with is small and the volume fraction of texture is large, the abnormal grain growth disappears; the average grain size is affected by the grain boundary migration, energy and the number of abnormal growth grains.Fifthly, a recovery & recrystallization model under variant temperature with clear physical fundamental was established, which is base on the grain growth MC model of textural material, the corresponding experiments and the existing 2D recrystallization model. In the new model: 1) initial mesoscopic stored energy field is constructed on the basis of the plastic deformation theory or the experiment of EBSD, respectively; 2) the subgrain abnormal growth nucleation and the relation between stored energy and texture are considered; 3) the theories of oriented nucleation and selective growth are used for different textural materials; 4) the effect of temperature changing on the recrystallization is introduced. For different reductions and annealing temperatures, the simulated results of recrystallization process using the model are consistent with the corresponding experimental ones, which reflect the real law of recrystallization.Finally, by combining the 2D grain growth model with the recrystallization model of textural material, a 2D annealing process model of textural material was obtained, in which the effects of texture on the microstructure evolution of recrystallization annealing is considered. The simulation researches and the experiments of annealing processes of ELC-BH steel plate and commercial pure aluminum (1060) plate are carried out, respectively. The results verify the rationality of the recrystallization annealing model for textural materials.