Mechanics and radiation tolerance of nanostructured steels for fusion plant structures

基于体心立方(BCC)结构的结构钢是托卡马克聚变堆第一壁部件的优先选择，因为它们具有更好的抗辐射诱导空穴膨胀和高温机械强度。例如，活性降低的铁素体/马氏体(RAFM)钢就是这种情况。不幸的是，这些传统的RAFM钢在&gt；550℃温度下热不稳定，其机械和蠕变强度恶化，可能无法满足其最低性能要求。一种替代方法是使用粉末冶金技术生产具有纳米级氧化物颗粒的bcc钢，即氧化物弥散强化(Ods)钢。然而，到目前为止，消耗臭氧层物质钢还不能以相对较大的成分生产出来，供核电界采用。此外，ODS钢的焊接会对原有的颗粒分布造成不良影响，导致任何反应堆部件在辐射和机械方面都存在弱点。本项目的重点是寻找一种新的有前途的替代传统RAFM钢和ODS钢的方法，即纳米结构钢。这些新型FM纳米钢的吸引力基于较大体积分数的热稳定细MX颗粒的存在，从而为650摄氏度的扩展操作限制打开了大门，并可能超过该温度。这些钢材还在这一领域提供了独特的优势，可以铸造成大部件。纳米结构钢的发展仍处于起步阶段，但它们最近已被标记为聚变托卡马克中结构部件的领跑者。该项目的目的是通过一种系统的方法，在与托卡马克设计的第一壁相关的环境条件下对纳米结构钢进行表征和性能测试，从而加速在聚变技术中采用纳米结构钢。向下选择的钢的化学成分和显微组织将使用分析电子显微镜进行深入表征。最有希望的钢将用离子辐照结合电子显微镜进行辐照测试，以原位观察原子迁移、局部化学偏析、纳米粒子稳定性和晶格缺陷的形核和演化。通过在高亮度同步加速器设施中进行现场力学测试，将实时监测塑性变形机制。这些设施只有在最近几天才能在材料被拉紧的情况下实时重建大块多颗粒结构。这些成果将被反馈到钢加工中，旨在加速纳米钢的部署，在第一壁融合结构中提供辐射和热机械载荷下的优化性能。在这个项目中，学生将获得一套独特的可转移技能，从编程到复杂样本环境的设计，数据挖掘，以及有效的沟通技能。学生还将获得钢铁冶金、多晶材料的塑性变形机制和颗粒重构技术的深入知识。

Structural steels based on body-centred cubic (bcc) structures are a preferential option for first-wall components in tokamak-type fusion reactors due to their enhanced resistance to radiation-induced void swelling and high-temperature mechanical strength. Such is the case for example of reduced activation ferritic/martensitic (RAFM) steels. Unfortunately, those traditional RAFM steels are thermally unstable at temperatures > 550 C and their mechanical & creep strength deteriorates, potentially not fulfilling their minimum performance requirements. One alternative approach is the use of powder metallurgy to produce bcc steels with nm-size oxide particles, namely Oxide Dispersion Strengthened (ODS) steels. However, ODS steels cannot be produced to date in relatively large components for their adoption in the nuclear community. Besides that, ODS steel welding causes non-desirable consequences to the original particle distribution, leading to weak points, both radiation and mechanically, for any reactor components.The focus of this project is on a new promising alternative to traditional RAFM steels and ODS steels, namely nano-structured steels. Those new FM nano-steels base their appeal on the presence of a thermally-stable population of fine MX particles in larger volume fractions, opening the door to extended operational limits of 650 C and potentially beyond that temperature. These steels also offer the unique advantage in this field of being castable into large components. The development of nano-structured steels is still in its very infancy, but they have recently been flagged as a frontrunner for structural components in fusion tokamaks. The aim of this project is to accelerate the adoption of nano-structured steels in fusion technology by a systematic approach to their characterization and performance testing in environmental conditions relevant for the first wall of tokamak designs. A down-selection of steel chemistries and microstructures will be characterized in-depth using analytical electron microscopy. The most promising steels will be radiation tested using ion irradiation in combination with a transmission electron microscope, in order to visualize in situ the atomic migration, local chemical segregations, nano-particle stability and the lattice defect nucleation and evolution. The plastic deformation mechanisms will be monitored in real time by performing in situ mechanical testing at high-brilliance synchrotron facilities. Those facilities allow only in very recent days to reconstruct the bulk multi-grain structure in real time as the material is being strained. These results will be retro-fed into steel processing, aiming to accelerate the nano-steel deployment, offering optimized performance under the radiation and thermo-mechanical loads in first-wall fusion structures. During this project, the student will acquire a unique set of transferrable skills ranging from programming to design of complex sample environments, data mining, and effective communication skills. The student will also gain in-depth knowledge about steel metallurgy, plastic deformation mechanisms in polycrystalline materials and grain reconstruction techniques.