熔盐环境下SiC/SiC复合材料力学性能退化机理研究

SiC/SiC composite has been an important candidate material in Molten Salt Reactor (MSR) due to its excellent high temperature mechanical properties, corrosion resistance and irradiation stability.However, the mechanical properties of SiC/SiC composites deteriorate under molten salt condition, which will affect the design of SiC/SiC composite structures. Early studies show the mechanical properties of SiC/SiC composites decrease as molten salt infiltrate internal pore structure in SiC/SiC composite and interact with the microstructure. The study on interaction between molten salt and SiC/SiC composite were focused on corrosion resistance of SiC materials. But so far, the mechanism of mechanical properties deterioration of SiC/SiC composite is still unclear. Therefore, combined with advanced 3D SR-μCT , in-situ load device, nanoindenter and SEM, damage or evolution of microstructure of SiC/SiC composites induced by corrosion, molten salt impregnation, crystallization and thermal expansion will be investigated. The effect of molten salt on microstructure evolution in SiC/SiC composite will also be studied. The present study is expected to identify the interaction between molten salt with microstructure in SiC/SiC composite. The mechanism of mechanical property deterioration of SiC/SiC composite will be revealed, which could guide process optimization and structural design of SiC/SiC composite for MSR.

由于具有优异的高温机械性能、耐腐蚀性、辐照稳定性，SiC/SiC复合材料成为熔盐堆重要的候选材料。然而，高温熔盐环境下，SiC/SiC复合材料力学性能会发生退化，影响其结构件的设计。前期研究表明，熔盐堆环境下，高温熔盐会浸入材料内部的孔隙结构，与其微观结构产生复杂的相互作用，导致材料力学性能下降。而高温熔盐与SiC/SiC复合材料相互作用研究，主要集中在抗腐蚀性方面。到目前为止，导致其力学性能退化机理还不清楚。基于此，本项目拟结合纳米压痕、SEM等表征手段，采用先进的同步辐射三维显微CT原位加载成像技术，研究腐蚀、熔盐浸渗、结晶与热膨胀对其微结构损伤的影响规律，以及载荷作用下熔盐在其结构演化中所起的作用。通过本项目研究，可明确高温熔盐与SiC/SiC复合材料微结构的相互作用，揭示SiC/SiC复合材料力学性能退化机理，为熔盐堆用SiC/SiC复合材料工艺优化和结构件设计提供指导。

SiC/SiC复合材料作为新型的核能高温结构材料备受关注。在熔盐堆中，高温熔盐与其接触时发生相互作用。本项目采用三维显微CT，结合SEM等表征手段对两维编织和三维编织结构SiC/SiC复合材料内部三维孔隙结构以及熔盐浸渗行为进行表征，结果表明：SiC/SiC复合材料孔洞受纤维预制体几何结构影响极大，熔盐仅存在于复合材料内部开孔孔洞，并且具有聚集结晶现象。通过Avizo软件对熔盐浸渗前后SiC/SiC复合材料孔隙率进行定量分析，经计算发现：由于腐蚀作用，熔盐浸渗后SiC/SiC复合材料小孔洞（≤10μm）数目具有增多趋势，而由于腐蚀与熔盐聚集结晶，复合材料内部大孔洞体积占比出现增加的趋势。通过SiC纤维与复合材料块体的熔盐腐蚀实验，分别研究了高温熔盐对SiC/SiC复合材料各相的腐蚀作用，并对腐蚀前后力学性能进行对比，结果表明：高温熔盐对SiC/SiC复合材料各相力学性能均有衰减作用，会导致熔盐环境下SiC/SiC复合材料力学性能下降。采用原位加载CT成像装置对两维编织结构SiC/SiC复合材料损伤过程进行研究，结果发现：SiC/SiC复合材料裂纹主要产生于孔洞密集的地方，尤其层间的大孔部位。熔盐浸渗会使复合材料孔洞孔隙率增大或增多，复合材料加载过程中，裂纹的产生于扩展主要集中在孔隙结构部分，因此熔盐浸渗后大大增加了SiC/SiC复合材料破坏的概率。通过对熔盐浸渗后SiC/SiC复合材料弯曲性能进行表征，也发现在熔盐存在的孔洞具有大量裂纹存在，表明熔盐浸渗对其力学性能退化起着关键性的作用。. 本项目研究，阐明了熔盐在SiC/SiC复合材料的浸渗行为以及熔盐与材料微结构相互作用，揭示了熔盐浸渗对SiC/SiC复合材料结构影响规律及机制，明确了熔盐环境下SiC/SiC复合材料力学性能退化机理，为SiC/SiC复合材料优化与熔盐环境下应用提供理论指导。