Isotope labeling for quantitative determination of defect sink strength and fundamentals studies on defect-sink interactions

核电是满足日益增长的能源需求的一种解决方案。在所谓的“核复兴”中，一个关键问题是在恶劣环境下向更长寿命发展的材料。为了抵抗高温下的中子损伤，人们通过引入缺陷槽来吸收/去除缺陷，从而开发了各种纳米结构材料。然而，缺陷沉陷强度的定量测定仍然是一个技术瓶颈。该项目使用同位素标记技术来定量测量离子辐照不锈钢中的吸收强度，这是全面研究缺陷-吸收相互作用的关键方法。这种能力对于开发耐辐射材料至关重要。即使对于相同类型的缺陷接收器，微调其微结构以最大化接收器强度也需要了解结构和接收器强度之间的一一对应关系。这项研究将有助于对金属中缺陷的总体理解。该项目为学生提供了独特的机会，将核工程、纳米材料、原子尺度表征和原子尺度建模方面的培训和研究结合起来，以解决现实世界中的重要问题。技术摘要对于天然铁丰度的铁基不锈钢，57Fe同位素原子的注入将引入57Fe间隙。退火后，57Fe在缺陷凹陷处的富集量直接反映了缺陷陷阱的凹陷强度。因此，可以系统地研究不同辐照/退火/应力条件下的缺陷沉陷强度。三维原子探针层析成像(APT)将用于绘制57Fe同位素分布图。将APT与透射电子显微镜和三维透射电子显微镜层析成像相结合，建立缺陷下沉结构与下沉强度之间的一一对应关系。本项目将研究两种缺陷沉陷类型：(1)晶粒工程不锈钢中的晶界，以了解晶界取向不良角对沉陷强度的影响；(2)氧化物弥散强化合金中的氧化物颗粒，以了解氧化物-基质界面对沉陷强度的影响。该项目进一步整合了分子动力学模拟，以揭示基本原理。缺陷汇强度将被用作动力学蒙特卡罗模拟的输入，以获得可以与实验观测相联系并与实验观测相比较的结构演化。结合材料合成、建模和原子尺度表征，该项目将获得最大限度地提高反应堆核心部件的辐射耐受性所需的基本理解。该项目为学生提供了独特的机会，将核工程、纳米材料、原子尺度表征和原子尺度建模方面的培训和研究结合起来，以解决现实世界中的重要问题。

Nontechnical AbstractNuclear power is one solution to meet the ever-increasing demand for energy. One key issue in the so called "nuclear renaissance" is materials development towards longer life time under harsh environments. In order to withstand neutron damage at high temperatures, various nanostructured materials have been developed by introducing defect sinks to absorb/remove defects. However, quantitative determination of defect sink strength is still a technological bottleneck. This project uses an isotope labeling technique to quantitatively measure the sink strength in ion irradiated stainless steels as a key approach for a full scope investigation on defect-sink interactions. Such capability is critical to develop radiation tolerant materials. Even for the same type of defect sinks, fine tuning of their microstructures to maximize sink strength requires knowledge of one-to-one correlation between structures and sink strength. The study will contribute to the general understanding of defects in metals. The project offers students unique opportunities to combine training and research in nuclear engineering, nanomaterials, atomic scale characterization and atomic scale modeling, for solving issues of real-world importance. Technical AbstractFor Fe based stainless steels of nature Fe abundance, implantation of 57Fe isotope atoms will introduce 57Fe interstitials. Upon annealing, the amount of 57Fe enrichments at defect sinks directly reflects the sink strength for defect trapping. Hence the defect sink strength under different irradiation/annealing/stress conditions can be systematically studied. Three-dimensional atom probe tomography (APT) will be used to map 57Fe isotope distributions. APT is coupled with transmission electron microscopy (TEM) and 3-D TEM tomography to establish one-to-one correlation between defect sink structure and sink strength. The project will study two defect sink types: (1) grain boundaries in grain-engineered stainless steels in order to understand effects of boundary misorientation angles on sink strength and (2) oxide particles in oxide-dispersion-strengthened alloys (ODS) in order to understand the effects of oxide-matrix interfaces on sink strength. The project further integrates molecular dynamics simulations to shed light onto fundamentals. The defect sink strength will be used as inputs in kinetic Monte Carlo simulations for obtaining structural evolutions which can be linked to and compared with experimental observations. In conjunction with materials synthesis, modeling, and atomic scale characterization, the project will obtain the fundamental understanding needed to maximize radiation tolerance of reactor core components. The project offers students unique opportunities to combine training and research in nuclear engineering, nanomaterials, atomic scale characterization and atomic scale modeling, for solving issues of real-world importance.