Phase Field And Crystal Plasticity Simulations And Related Coupled Models Of Microstructure Change And Deformation In Metals

Deformation was influenced largely by the internal state of materials, such as second phase, morphology and orientation of grains, etc., whereas, these internal states were also influenced by the process of deformation. So, it is necessarily to study the evolution of morphologies, the deformation rules of crystals, and espectively, the coupling of morphology and crystal deformation process. And moreover, by the way of computational simulation, more detailed information can be got than experiment. In the first part of this work, several morphologies have been simulated by the way of phase field methold, includeing several diffusional and structural phase transformations, and the evolution of dislocation under external stress. In the second part, crystal plasticity simulation was performed on metal polycrystal, the influence of mesh parameters on simulation results was studied. And in the last part, coupled modle of morphology evolution and crystal deformation was established with the form of FEM expressions.In the simulation of diffusional phase transformation, a coupled model of micromagnetic method and phase field method has been established to study the spinodal decomposition precess of feromagnetic alloys under an external magnetic field. Result shows the ability of external magnetic field to elongating precipitates along its direction. So, one can control the morphology of decomposition through the controlling of the direction of external maignet field. Three different modles of anistropic gradient energy have been proposed in this section. Using these modles, one can easly simulate the formation process of polygonal phase in 2D and polygonal diskshape or rodshape phase in 3D. In the simulation of structural phase transformation, a new recrystallization modle was proposed in the framework of phase field method. In this modle, recrystal grains were nucleated at grain boundaries preferentially, and the relative nucleation probability inside grain increase with the increase of temperature and stored deformation energy. The second power of growth rate of recrystal grains linear increase with stored energy. The proposed recrystallization modle can also be used when existing of second particles. Result shows that the exist of second particles increases the nucleation rate, however, it also pined the moving of grain boundary of recrystal grains. In the last part of this section, evolutions of dislocation were simulated using a phase field dislocation modle, the slip, cross slip and multiplication of dislocation, the reactions between different dislocations, and the interaction between dislocation and second particles were simulated, results were consistant with the classical dislocation theory.In the simulation of deformation process of metal polycrystals, new algorithms of the generation of polycrystalline structures and meshing of these structures were porposed. In these algorithms, the generation and meshing of polycrystals were automatically executed according to the parameters gived. The proposed algorithms were extraordinary convenient when large number of grains were employed in the aggregate. Special attention of this part of work was paid to the sensitivity of simulation with respect to the mesh refinement. Results show that according to the length scale involved, different requirements on meshes were required, a coarse mesh containing about 500 grains was sufficient to predict the global stress-strain curve, with only one element per grain. About 5 elements per grain was enough to well describe the intergraunlar heterogeneities. However, at least 30 and 60 elements per grain should be used, in order to well describe the average deformation of each grain and to capture most of the intragraunlar heterogeneities, respectively. The simulation of deformation process of pure aluminum shows that, during the deformation, orientations of grains were gradually rotated. In polycrystal, deformation processes of different part in a sime grain were different. Duo to the noncontinue across grain boundaries, obvious stress concentration exist near grain boundaries, which leads to the earlier activation of dislocations in these regions than other regions, and with futher deformation, these activation areas were spread into grains.In the last part of this work, a coupled FEM modle was established based on the work of morphology simulation and crystal deformation simulation. The established modle can be used in following case, i.e., deformation when other pahse already exist but no evolution; deformation coupled with diffusional pahse transformation; deformation coupled with structural pahse transformation; and deformation coupled with mutiphase transformation. Especially, evolution of dislocations in the condition of deformation constraints can also be simulated use this modle, since it can also be treated as a special structural phase transformation in the framework of phase field method.