凝固过程晶粒生长动力学及拓扑转变机制的相场研究

Phase-Field Study for the Growth Kinetic and Topology Transformation Mechanism of Grains during Solidification Process

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 continuum phase-field dynamic model, the microstructure evolution, dynamics change and topology transformation during the solidification process of nucleation, growth and coarsening were studied, and the relationship between nucleation and growth was analyzed. Results show that volume fraction gradually increases to the equilibrium value, while the total surface area of grains increases first and then decreases during the process of nucleation and growth. For nucleation, volume free energy is driving force and surface energy is resistance force. Nucleation process is accompanied by growth process; these two processes are overlapped and competed During the growth process, grains with more than six sides continue to grow, and that with less than six sides gradually reduces. The mechanisms of small grain disappearing are neighbor switching mechanism, direct annihilation mechanism of three, four and five sided grains, the intersection of four sides separated and resulting in the disappearance of small grain, and direct disappearance mechanism of grain boundary. The simulation results are in good accordance with experiment results.