Research On The Microstructure Simulation Of The Alloy Solidification Based On Phase Field Method By The Octree Mesh Technology

The numerical simulation of the solidification microstructure is subject to a growing body of research because of the ability of showing the processing of the solidification microstructure transformation in grains as well as finer size, predicting the microstructure of the casting and evaluating the mechanical properties of the casting. Based on the diffuse interface model which makes the interface as a continuous interface with certain thickness and avoids to track the complicated interface, the phase-field method as a numerical simulation tool is applied widely in the numerical simulation of the solidification microstructure, including from the pure metal to the multicomponent alloy, from the two dimension to three dimension, from the eutectic to peritectic and so on. The computation used for this method is the bottleneck for its further development. And the focus of this paper is how to improve the computation efficiency and reduce the computation resource when the phase field method is used for the numerical simulation of the solidification microstructure.Firstly, the adaptive mesh technology based on octree is research with the five aspects of the relationship, the data structure, formation rules, the traversal operation and the adaptive mesh. The mathematical model of the phase field method is established including the pure metal model, the binary alloy model, the anisotropic and the multi-grain technology. The control equation of the phase field, the concentration and the temperature are discretization by the technology of the first and multi-order derivative gained in the octree mesh. The method which the computation is done on the same level value cells is first proposed in this research. And it can solve the problem which the diffusion coefficient of the temperature and the concentration is not the same order. Based on the distance technology, this research gives the adaptive mesh generation mesh based on the octree. The method to obtain the position and the value of the mesh point in the post processor and the parallel computing techniques are also discussed in this research.Secondly, the numerical simulation results of the single equiaxed grain growth of the pure metal are given. Contrast with the results using the uniform mesh, it can conclude the phase field with the adaptive mesh based on the octree which established in this paper has the ability not only to do the simulation of the solidification microstructure, but a great improvement for the computation and reduction the resource. The efficiency of the parallel and the affection of mesh parameters to the solidification microstructure are also discussed in this paper. Then this research gives the research on the relationship of the thermophysical parameters with the dendritic morphology of the equiaxed and columnar grams.Thirdly, this paper gives the research on the numerical simulation of the isothermal and non-isothermal solidification of the binary alloy. It can be gained from the results that the phase-field model with adaptive mesh based on the octree can be applied well to the simulation of the solidification microstructure of the binary alloy. And the variation of the microsegregation of the binary alloy from the simulation results and the simulation results of the multi-columnar grains growth also gives the conclusion.At last, two experiments including the organic solution crystallization and the metallographic experiment of the aluminium alloy casting are used to verify the simulation results of the solidification microstructure of the pure metal and the binary alloy. It is showed the simulation results and the experimental results are comparable in the fuse of the columnar grain of the pure metal and the dendritic growth of the binary alloy.