两相复合燃料烧结末期晶粒长大过程的相场模拟

Phase-Field Simulation of Grain Growth During Final Stage of Sintering in Two-Phase Composite Fuels

摘要:

本研究基于相场方法构建了两相复合燃料烧结末期晶粒长大过程的数值模型，并系统模拟了UO₂-UN复合燃料体系的晶粒演化行为。首先，通过建立双晶粒夹持空洞的简化模型，揭示了晶界与空洞的交互作用机制。研究表明：晶界附近空洞呈现收缩动力学特征并形成透镜状形貌，且与高界面能晶粒接触的空洞收缩速率显著提升；体系的三重界面角由两相晶界能与界面能的比值决定。其次，针对两相多晶体系的晶粒长大过程进行定量分析，相体积分数影响研究表明：相界面对晶粒迁移具有显著制约作用，随着第二相体积分数增加，相界面密度增大导致晶粒生长速率衰减。最后，构建两相多晶含空洞体系晶粒长大模型，对空洞产生的钉扎效应进行研究并阐明烧结末期的生长动力学机制，空洞钉扎效应研究表明：空洞对晶界产生钉扎作用，其钉扎强度与孔隙密度呈正相关，且局部空洞分布的非均匀性将诱发异常晶粒生长现象，三维空洞钉扎分析显示：复杂的晶粒拓扑结构强化了空洞的钉扎效应，使得异常晶粒生长在三维体系中呈现更显著的形貌特征。

Abstract:

A numerical model based on phase-field method to simulate the grain growth during the final sintering stage of a two-phase UO₂-UN composite fuel was established, systematically investigating the grain evolution within the composite fuel system. Firstly, a simplified model of a void held between two grains was established to elucidate the interaction mechanism between grain boundary (GB) and voids. The results show that voids near GBs exhibit shrinkage dynamics and evolve into a ellipsoidal shape. Additionally, voids in contact with grains of high interfacial energy show significantly accelerated shrinkage rate. The triple interface angle in the system is determined by the ratio of the two-phase GB energy to the interface energy. Furthermore, a quantitative analysis was conducted on the grain growth process within the two-phase polycrystalline system. The investigation into the effect of phase volume fraction reveals that grain migration is significantly constrained by phase interface. As the volume fraction of the secondary phase increases, the increased phase interface density reduces the grain growth rate. Finally, the grain growth model for the two-phase polycrystalline system containing voids was developed to investigate the pinning effect induced by voids and to elucidate the growth kinetics at the final sintering stage. The results show that voids induce GB pinning, with the pinning strength positively correlated with void density. Non-uniform local void distribution can trigger abnormal grain growth. A three-dimensional void pinning analysis further shows that complex grain topology enhances the void pinning effect, resulting in more distinctive morphological features of abnormal grain growth in three-dimensional systems.