动态应变时效对15-15Ti包壳在液态铅铋中低周疲劳断裂影响机制研究

Lead-bismuth eutectic (LBE) is considered as the main candidate coolant for Accelerator Driven Sub-critical System. However, LBE would reduce the mechanical properties of nuclear structural materials, especially for the fatigue property. 15-15Ti is selected as the cladding material for sub-critical reactor in ADS. Dynamic strain ageing (DSA), which is considered as an important issue to influence the fatigue property, occurs during the operation of the reactor. The research about the effect of LBE on the fatigue of austenitic stainless steel is very limited, and DSA has not been discussed so far. Therefore, it is necessary to understand the influence of DSA for the fatigue property of 15-15Ti in LBE environment. This project intends to compare the difference between the fatigue properties of 15-15Ti in vacuum and LBE, and deduces the influence of DSA and LBE to the fatigue property of 15-15Ti. In addition, the influence of DAS and LBE on the initiation and propagation processes of fatigue crack in different stages is analyzed by SEM, EBSD and TEM methods. The interaction effect of DSA and LBE on the fatigue facture mechanism is concluded from the above results. This research could provide the theoretical guidance and experimental supports for the assessment of cladding tubes and the verification of fuel assembly.

液态铅铋合金（LBE）作为加速器驱动次临界系统的主选冷却剂材料，会降低反应堆结构材料的力学性能特别是疲劳性能。15-15Ti作为ADS次临界反应堆的主选包壳材料，在反应堆运行时会产生动态应变时效（DSA），DSA对疲劳性能也存在显著影响。目前针对奥氏体不锈钢在LBE中的疲劳性能研究较少，且没有涉及到DSA的影响。因此DSA对15-15Ti包壳在LBE中的疲劳断裂的影响机制有待于深入研究。本申请项目拟针对15-15Ti的疲劳断裂机制，开展真空及LBE环境的疲劳试验研究，获得DSA及LBE对15-15Ti疲劳性能的影响；同时通过SEM、EBSD、TEM等技术研究疲劳过程不同阶段的萌生及扩展过程，阐述DSA及LBE对疲劳裂纹萌生及扩展的影响规律，揭示DSA及LBE交互作用对15-15Ti疲劳断裂的影响机制。该研究成果可为铅铋堆包壳服役评价以及燃料组件验证提供了理论指导和实验支持。

15-15Ti是铅铋冷却反应堆的主选包壳材料，包壳在运行时受到交变载荷的影响产生疲劳损伤。15-15Ti在反应堆运行工况下会产生动态应变时效（DSA），从而引起疲劳性能的下降，同时液态金属铅铋（LBE）与包壳长时间接触也会降低其疲劳性能，因此DSA对15-15Ti包壳在LBE介质中疲劳断裂的影响机制是制约15-15Ti包壳工程应用的重要科学问题。.本项目以15-15Ti奥氏体不锈钢为研究对象，开展了15-15Ti在真空及LBE介质环境下的低周疲劳实验研究，获得了DSA和LBE对15-15Ti宏观疲劳力学性能的影响规律；结合显微组织分析，揭示了真空中实验温度对15-15Ti疲劳裂纹扩展速率的影响规律，阐述了LBE介质中DSA和LBE的交互作用对15-15Ti疲劳裂纹萌生和扩展的作用机制。主要结果为：(1) DSA效应使得试样表面局部应力增加，裂纹源数目变多；(2) 15-15Ti在LBE中的疲劳寿命较真空下有所降低；(3) DSA和LBE交互作用使得疲劳裂纹扩展方式由穿晶扩展变成沿晶和穿晶共同主导的扩展方式。.研究成果对于揭示奥氏体材料在液态金属中的疲劳行为具有重要借鉴意义，同时为铅铋堆包壳服役评价以及燃料组件验证提供了理论指导和实验支持。