Irradiation Damage in Tungsten alloys

适用于核聚变反应堆偏滤器的材料需要能够承受高热负荷（高达20 MW/m2）、高瞬态应力水平和高水平的中子辐照损伤。这使得它成为任何材料必须生存的最极端的环境之一。主要的候选材料是钨，因为它的熔点高，并且对等离子体侵蚀具有良好的抵抗力。然而，其机械性能差，并且缺乏关于它们如何被中子辐照降解的知识。众所周知，中子辐照对钨有两个主要影响。1)对晶格的损伤导致缺陷，例如空位、位错环和空隙，以及2）转化成不同的元素，这导致高达5%的钨变成铌、锇、钽和其他微量元素。由于原始元素和转化元素与晶体缺陷相互作用而导致的微观结构的聚集和演化决定了诸如延展性和导热性的重要性质。多元素的相互作用是相对未知的，因为大多数研究现在都集中在纯钨或二元合金上。特别是，不同的嬗变产物如何相互作用尚不清楚。一些已知的集群，但其他人可能反隔离。这方面的知识是需要的，如果模型的辐照损伤过程中要开发，可以包括现实的嬗变微观结构。将研究两种辐照样品：1）离子辐照样品，其被预合金化以具有预测在未来聚变反应堆中产生的WReTaOs水平。这些样品已在美国LANL和英国萨里进行了辐照，2）来自裂变反应堆（荷兰HFR、比利时SCK-CEN和波兰Maria）的中子辐照样品。离子辐照模拟中子辐照的效果如何是一个悬而未决的问题，我们将在本项目中回答这个问题。本项目将使用原子探针层析成像（APT）在单原子长度尺度上进行化学分析，并将观察到的化学结构与透射电子显微镜中成像的晶体缺陷相关联。将重点发展相关技术，以直接成像TEM和APT中相同的缺陷。将使用CCFE和牛津大学新安装的用于活性材料研究的设备对中子辐照样品进行研究。这包括该国第一个主动原子探测器。将使用新开发的纳米压痕方法来映射大面积（几平方毫米）的微观结构损伤对机械性能的影响进行研究。这将使钨合金的离子和中子损伤之间的差异的理解，并开发方法来预测中子辐照的微结构使用替代辐照。学生将接触到广泛的实验技术和数据分析方法，并学习在活性材料上工作。该项目与能源和核聚变EPSRC领域保持一致。

Materials suitable for use in the divertor of a nuclear fusion reactor need to be able to withstand, high heat loads (upto 20MW/m2), high transient stress levels, and high levels of irradiation damage from neutrons. This makes it one of the most extreme environments for any material to have to survive in. The leading candidate material is tungsten due to its high melting point, and good resistance to plasma erosion. However its mechanical properties are poor and there is a lack of knowledge on how they are degraded by neutron irradiation. It is well know that neutron irradiation will have two major effects on the tungsten. 1) damage to the crystal lattice leading to defects such as vacancies, dislocation loops and voids and 2)transmutation in to different elements which leads to upto 5% of the tungsten becoming rhenium, osmium, tantalum and other minor elements. The clustering and evolution of the microstructure due to the original and transmuted elements interacting with the crystallographic defects determines important properties like ductility and thermal conductivity. The interaction of multiple elements is relatively unknown as most research to now has focused on pure tungsten or binary alloys. In particular how the different transmutation products interact with each other is unclear. Some are known to clusters but others may antisegregate. A knowledge of this is need if models of the irradiation damage process are to be developed that can include realistic transmutation microstructures. Two sorts of irradiated samples will be studied 1) ion irradiated samples which are pre-alloyed to have WReTaOs levels predicted to be produced in future fusion reactors. These have been irradiated at LANL in the USA and Surrey in the UK and 2) neutron irradiated samples from fission reactors (HFR Holland, SCK-CEN Belgium and Maria, Poland). How well the ion irradiations mimic the neutron irradiation is an open question and one we will answer with this project.This project will use atom probe tomography (APT) to perform chemical analysis at the single atom length scale and relate the chemical structures observed to crystallographic defects imaged in the transmission electron microscope. There will be a focus on developing correlative techniques to directly image the same defects in TEM and APT. Neutron irradiated samples will be studied using newly installed equipment at CCFE and Oxford for the study of active materials. This includes the countries first active atom probe. The effect the microstructural damage has on mechanical properties will be studied using newly developed nanoindentation methods to map large areas (several mm2). This will then allow an understanding of the differences between ion and neutron damage in tungsten alloys and to develop methods to predict neutron irradiated microstructures using surrogate irradiations. The student will be exposed to a wide range of experimental techniques and data analysis methods and learn to work on active materials. This project is aligned with the energy and nuclear fusion EPSRC areas.