15-15Ti不锈钢的液态铅铋腐蚀蠕变行为和失效机理研究

15-15Ti austenitic stainless steel is one of the most important fuel cladding candidate materials for accelerated driven system coupled liquid lead-bismuth eutectic (LBE) cooled fast reactors. Its compatibility with LBE coolant has been extensively studied, but the understanding of the corrosion creep behavior and failure mechanism is not clear yet. This project is aimed to investigate the corrosion creep behavior of 15-15Ti exposed to LBE and explore the influence of multiple parameters such as stress, temperature and oxygen dissolved in LBE and cold deformation on Ni dissolution rate and creep properties. Advanced characterization techniques are employed to examine fractography, oxide structures, chemical composition and phase constituents at Ni dissolution induced ferritization phase transformation regions, corrosion microstructures at crack tips, distribution of Pb and Bi atoms at mechanical twin boundaries. First principle is employed to study electric charge distribution and bonding characteristics after Pb and Bi atoms are introduced into the twin boundaries. All of the results are used to get deep insights into the underlying mechanisms of surface crack nucleation and propagation facilitated corrosion creep failure. The results are expected to contribute not only to lead-cooled fast reactor cladding material selection program and nuclear safety performance evaluation, but also to new corrosion-resistant material development program.

15-15Ti奥氏体不锈钢是加速器驱动液态铅铋共晶合金（LBE）冷却快堆最重要的候选核燃料包壳材料之一，其与LBE介质的相容性是近年来国内外研究的热点，但对其在LBE中的腐蚀蠕变行为和失效机理的认识还十分欠缺。本项目拟开展15-15Ti在LBE介质中的腐蚀蠕变研究，探索应力、温度、溶解氧含量和冷加工变形等参数对溶镍腐蚀速率和蠕变性能的影响规律；利用先进材料表征测试手段，深入分析断口形貌、氧化膜结构、溶镍腐蚀诱导铁素体相变区的化学成分和相组成、裂纹尖端腐蚀微观特征、Pb和Bi原子在孪晶界上的分布状态等，并结合第一性原理计算孪晶界上引入Pb和Bi原子后的电荷分布和成键特性，从多尺度深层次揭示高温、应力和腐蚀耦合条件下裂纹萌生扩展促进蠕变失效的微观机理。研究成果将对铅基快堆包壳材料选型与核安全性能评价提供重要数据参考，并为LBE腐蚀防护新材料的开发打下理论基础。

液态铅铋共晶合金具有优异的热工水力、中子学和本征安全性，是液态铅铋冷却快堆和加速器驱动核嬗变堆重要的冷却工质和散裂靶材料。但是，不锈钢在高温液态铅铋环境中存在相容性问题，这些问题主要包括液态铅铋腐蚀和脆化，导致材料性能发生严重退化。奥氏体不锈钢15-15Ti是液态铅铋快堆包壳的重要候选材料，其在铅铋环境中的性能对燃耗深度和反应堆的运行安全具有重要影响。为了理解不锈钢在铅铋中的服役性能，特别是在应力和铅铋腐蚀协同作用下的性能特点，本项目开展了铅铋环境下的蠕变实验，利用多尺度材料表征技术系统分析了腐蚀层结构和裂纹萌生扩展规律，揭示了不锈钢的失效规律。此外还开展了第一性原理计算，在电子尺度分析了Pb和Bi等元素对Fe的孪晶界能、表面能、弹性模量和断裂韧性等参数的影响规律，进一步加深了铅铋对铁基材料的影响规律。在此基础上，还对比研究了铁素体不锈钢和FCC+BCC双相多主元合金在液态铅铋环境中的力学失效规律，这些对比结果加深了15-15Ti奥氏体不锈钢在铅铋中的力学失效微观机理。本项目获得的实验结果一方面对新材料研发具有指导意义，还对国内铅铋快堆的工程化提供了重要数据支撑。