氮化铀压力辅助烧结过程的相场模拟

Phase Field Simulation of Pressure-Assisted Sintering Process of Uranium Nitride

摘要:

通过引入弹性应变能和颗粒刚体运动过程，建立了UN压力辅助烧结过程的相场模型，分析了应力对烧结颈增长过程、颗粒刚体运动对孔隙收缩过程的影响，并模拟了物质扩散、刚体运动与应力共同作用下的多颗粒烧结过程。模拟结果表明，烧结颈长度及其增长速率随施加应变的增大而增大，在烧结颈两端出现明显的应力集中现象，且随着时间的延长，应力分布逐渐均匀化；随着平移迁移率的增加，孔隙收缩速率增大，其致密化完成时间提前，而转动迁移率的取值对孔隙收缩过程几乎无影响。本模型能够捕捉到烧结颈的形成和增长、孔隙的球化和闭合过程，大体积孔隙表面配位的晶粒数更高，存在时间更长。

关键词:相场模拟;氮化铀;压力辅助烧结;晶界扩散;弹性应变能

Abstract:

The pressure applied during the sintering process plays an important role in improving the final density of UN pellets. In this work, a phase field model of UN pressure-assisted sintering was established by introducing elastic strain energy and particle rigid motion process. The effects of stress on the growth of sintering neck and rigid-body motion on the pore shrinkage were analyzed, and the multi-particle sintering process under the three mechanisms was simulated. The simulation results show that the length of the sintering neck and its growth rate increase with the increase in the applied strain. There is obvious stress concentration at both ends of the sintering neck, and the stress distribution gradually becomes uniform with the increase in time. With the increase in translational mobility, the pore shrinkage rate increases, and the densification completion time is advanced, while the value of rotational mobility has little effect on the pore shrinkage process. The model can capture the formation and growth of the sintering neck, the spheroidization and closure of the pores. The coordination grain number of large volume pores is higher and the existence time is longer.

Key words:phase-field simulation;uranium nitride;sintering;pressure-assisted sintering;grain boundary diffusion;elastic strain energy