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基于连续相场动力学模型,研究了凝固过程形核、长大及粗化阶段的组织形貌演化,动力学转变,以及粗化过程拓扑转变,分析了形核与长大过程的关系。研究结果表明,形核长大过程中,晶粒体积分数逐渐增大至平衡值,总表面积先增大后减小,体积自由能是形核的驱动力,表面能是形核的阻力。形核伴随着长大,两者是相互重叠相互竞争的两个过程。晶粒生长过程中,边数大于六的晶粒持续长大,而边数少于六的晶粒不断缩小。小晶粒消失机制有:临近切换机制;三边﹑四边及五边晶粒直接消失机制;四边交叉点分离并最终导致小晶粒消失机制;晶界直接消失机制。模拟结果与实验结果符合较好。
Based on the kinetic model of continuous phase field, the evolution of morphology, dynamics and topological transformation in the process of nucleation, growth and coarsening were studied. The relationship between nucleation and growth was analyzed. The results show that in the process of nucleation and growth, the volume fraction of grains gradually increases to the equilibrium value, the total surface area first increases and then decreases, and the volumetric free energy is the driving force of nucleation. The surface energy is the resistance of nucleation. With the nucleation and growth, the two are mutually overlapping and competing processes. During grain growth, grains with more than six edges continue to grow, whereas grains with fewer than six edges continue to shrink. The mechanisms of disappearance of small grains are: the near-switching mechanism; the mechanism of direct disappearance of grains on three sides, four sides and five sides; the separation of four sides and finally the disappearance of small grains; and the direct disappearance of grain boundaries. The simulation results are in good agreement with the experimental results.