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本工作建立了陶瓷型复合燃料两相烧结过程的相场模型，利用该模型模拟了UN-U3Si2复合燃料的烧结过程。首先，研究了两相双晶粒在烧结过程中的烧结颈的演化过程。结果表明，具有较高表面能的晶粒在烧结颈形成过程中的表面形变更明显；两相双晶粒形成的平衡二面角的大小取决于两相的晶界能与表面能的比值；两相不等大的双晶粒之间未发生大晶粒吞噬小晶粒现象。然后，研究了烧结过程中的两相三晶粒之间的气孔收缩和三叉晶界的演化，以揭示符合燃料烧结过程中气孔的演变规律。结果发现，两相三晶粒形成的三叉晶界夹角偏离了120°，晶界处的高能势垒阻碍了气孔的空位沿晶界的扩散，导致三叉晶界处的气孔收缩速率减慢。最后，研究了两相陶瓷型复合燃料的多晶烧结过程。不同体积分数比的两相多晶烧结组织形貌演化的模拟结果表明，晶界扩散在两相烧结过程中起主要作用，体积分数较大的相的晶粒生长占据主导地位，两相晶粒之间存在阻碍晶界迁移的作用，同相晶粒之间存在晶粒迁移现象。Due to the inadequacy of the existing experimental techniques, it is difficult to observe the microstructure evolution during the sintering process in real time, resulting in a lack of in-depth understanding of the sintering mechanism of two-phase composite fuels. Therefore, it is greatly important to carry out theoretical simulation studies on the sintering process of composite fuels. In this work, a phase-field model of the two-phase sintering process of ceramic composite fuel is established, and the sintering process of UN-U3Si2 composite fuel is simulated by using this method. The simulation results show that the surface deformation of the grains with higher surface energy is obvious during the formation of sintering neck. The final equilibrium dihedral angle formed by the two-phase double grains depends on the ratios of the grain boundary energy to the surface energy of the two phases. The phenomenon of large grains swallowing small grains do not occur between the two unequal double grains. Subsequently, the pore shrinkage and the properties of the trident grain boundary between the two-phase three-grain are investigated during the sintering process. It is found that the angle of the trident grain boundary formed by the two-phase three-grain deviates from 120°. The high-energy barrier at the grain boundary impedes the diffusion of the pore vacancies along the grain boundary, resulting in a slowdown of the pore shrinkage rate at the trident grain boundary. In addition, the simulation results of the microstructure evolution of two-phase polycrystalline sintered tissue with different volume fraction ratios show that the grain boundary diffusion plays a major role in the two-phase sintering process. The grain growth of the phase with a larger volume fraction is dominant, and the role of hindering the grain boundary migration between the two-phase grains exists. The phenomenon of grain migration exists among grains of the same phase.
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Keywords:
- Phase field simulation /
- Composite fuel /
- Sintering /
- Grain growth /
- Grain boundary and interface boundary
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