Computer Simulation Of Order-Disorder Phase Transformation In Alloy And Grain Growth By Phase Field Method

Phase-field method, as a method of simulating material microstructure evolution, has been applied to all common microstructure evolution simulation. It can simply characterize the geometric shape of any complex organization also can simulate different microstructure evolution such as: nucleation growth and coarsening in the same physical and mathematical model. So phase-field method has been the preferred method for computer simulating material microstructure evolution, just like solidification and dendrite growth, Ostwald pirening, Spinodal decomposition, order-disorder phase transformation, Martensitic transformation, grain growth and so on. In this thesis, we study Macro-phase field and Micro-phase field in the field of grain growth and alloy precipitation precipitates microstructure evolution.First, the normal grain growth under the condition of single phase was simulated in 2D by means of the macro-phase field method. The effectiveness of the phase-field method was proved. The results show that the phase-field model accords with the classic model of growth, and grain size distribution which can well described by Weibull function is time-dependent. On this basis, we study grain size and grain size distribution which are affected by the value of the potential well parametersγand the energy gradient coefficient K_i. Conclusion: first, theγ-value greater inhibit grain growth, with the increase of K_i, grain growth accelerated, and by theformation of grain boundaries and the more thick. Second, the atomic-scale computer simulation of order-disorder phase transformation is conducted under the micro-phase field model. We choose Al₃Li alloy as a specificstudy and researchδ′precipitation precipitates. We discuss the mechanism ofδ′precipitation and find the coarsening behavior ofδ′is taken place as the same time as the growth of order-phase.