Multiscale high-temperature mechanical performance of materials for nuclear fusion

核聚变现在正被认真考虑作为2050年后的未来能源，正如诺丁汉郡最近宣布的STEP建设所证明的那样。了解中子的辐照损伤如何影响结构材料的机械性能是实现核聚变作为可持续能源的关键一步。如果不了解中子损伤对材料的影响，就没有切实可行的方法来延长反应堆部件的寿命。然而，我们不能仅仅建造一个反应堆来测试材料，然而，研究辐照材料是昂贵的，从它们中产生机械数据是困难的。离子辐照可以模拟中子损伤，但损伤层很薄，只有200 ~ 100微米。因此，传统的力学试验方法已无法使用，必须进行新颖的微力学试验。由于测试小材料体积时固有的尺寸效应，这导致解释结果的困难。正在开发的机械模型将包括辐照损伤对不断变化的机械性能的影响，但这些需要大量的实验输入，以表征和机制理解不同的微观结构特征（空洞、沉淀、循环）如何控制辐照诱导硬化。该项目旨在对一系列模型合金进行微观力学测试，以消除不同微观结构特征的影响。合金的铬、碳和钒的含量将受到控制，以控制固溶体、间隙和碳化物的强化。样品将被重离子和氦照射以产生空洞和位错环。将在室温和工作温度下使用纳米压痕研究硬化。室温下的纳米压痕是研究辐照硬化的标准方法，但利用纳米压痕研究高温辐照硬化的工作却很少。我们期望利用牛津大学新开发的计算塑性有限元方法，我们将看到辐照损伤不仅对屈服应力有影响，而且对加工硬化也有影响。为了了解初始微观结构、辐照下的微观结构演变以及弹体位错与微观结构特征的相互作用，将采用先进的电子衍射成像技术。这将包括衍射对比透射电镜，这是为研究这种微观结构而建立的，还有传输菊池衍射，它很少应用于研究辐射损伤，但具有更简单和更便宜的成像设备的优势。我们预计，在项目结束时，我们将产生一系列的微观结构，对它们进行辐照，机械测试，并将硬化与观察到的微观结构联系起来。这将被输入到UKAEA新开发的模型中。该项目是与UKAEA/Culham聚变能源中心合作的，博士生将成为EPSRC聚变科学与技术CDT的一部分。该研究项目与EPSRC的投资组合主题“能源”以及副主题“聚变”和“核电”保持一致。“工程”主题也与“材料工程-金属和合金”研究领域相关。

Nuclear fusion is now being seriously considered as future power source for post 2050, as demonstrated by the recent announcement of the STEP construction in Nottinghamshire. Understanding how irradiation damage from neutrons affects the mechanical properties of structural materials is a key step towards realising nuclear fusion as a sustainable power source. Without understanding the effect that neutron damage has on the materials there is not realistic method of lifing components hence reactors. However we cannot just build a reactor to test materials and however, working on irradiated materials is costly, and generating mechanical data from them is difficult. Neutron damage can be simulated with ion irradiations but the damage layers are thin - 200 nm to 100 um. As such traditional mechanical testing methods cannot be used and novel micro-mechanical tests must be conducted. This leads to difficulties in interpreting the results due to size effects inherent in testing small material volumes. Mechanical models are being developed that will include the effect of irradiation damage on the evolving mechanical properties, but these require substantial experimental input in the form of characterisation and mechanistic understanding of how different microstructural features (voids, precipitates, loops) control irradiation induced hardening. This project will aim to use micromechanical testing on a series of model alloys to deconvolute the effects of different microstructural features. The alloys will be cast with controlled levels of chromium, carbon, and vanadium, to allow control of solid solution, interstitial and carbide strengthening. Samples will be irradiated with both heavy ions and helium to generate voids and dislocations loops. Hardening will be studied using nanoindentation at both room and operational temperatures. Nanoindentation at room temperature is a standard method of studying irradiation hardening but much less work has been carried out on high temperature irradiation hardening using nanoindentation. We expect that using newly developed computational plasticity finite elements methods developed in oxford we will see the effect off irradiation damage not just on yield tress but also work hardening. To understand both the starting microstructure, the microstructural evolution under irradiation and the interaction of the glissile dislocations with microstructural features advanced electron diffraction imaging will be used. This will include diffraction contrast TEM which is well established for studying such microstructures and also transmission Kikuchi diffraction which is much less applied to studying radiation damage but has the advantage of simpler and cheaper imagining equipment. We expected that byt the end of the project we will have gnateatered a range of microstructures, irradiated them, mechanically tested them and related the hardening to the observed microstructures. This will then be inputed to newly developed models at UKAEA. The project is in collaboration with the UKAEA/Culham Centre for Fusion Energy and the DPhil student will be part of the EPSRC CDT on the Science & Technology of Fusion. The research programme aligns with the EPSRC portfolio themes of both 'Energy' and the sub-themes 'Fusion' and 'Nuclear Power'. The 'Engineering' theme is also relevant through the 'Materials Engineering - Metals and Alloys' research area.