Structural integrity characterisation of nuclear materials via nano additive manufacturing

在我们着手建造先进的第四代核系统和聚变核系统之前，我们需要了解新材料在高辐射和高温下的行为。然而，健康和安全问题使我们无法在实验室中测试宏观机械辐照优惠券。解决方案是测试非常小体积的辐照材料，即微机械试件，并使用多尺度建模来推断宏观机械部件的测量行为。因为它们的体积很小，所以即使在低或中等活性水平的照射下，这种样品也可以在实验室进行测试。这提供了对多个试件进行测试以研究随机效应的可能性，例如，辐照对延性向脆性转变的影响。制造技术正在快速地从减法向加法转移。加法制造可以产生到目前为止使用传统减法(例如铣削)方法无法实现的几何形状。到目前为止，加法制造的进步还没有在微机械测试中得到复制。目前，制作微机械贴片的常用方法是利用镓或氦聚焦离子束(FIB)进行微细加工。在FIB研磨中，氦或镓的带电离子集中在样品上，以预定的几何形状溅射母材料，直到研磨出所需的形状。减法FIB球磨不仅不能代表可预见用于未来核完全制造的添加剂制造，而且还会在球磨的微机械样品中留下氦气泡或镓注入等损伤。因此，开发一种新的方法来制造不受FIB损伤(即氦或镓注入，或者在严重情况下，母材料非晶化)的微机械测试片是非常有必要的。在这项可行性研究中，我们将研究最初为可调光学系统开发的一种新的纳米添加剂制造方法在制造微机械样品方面的适用性。我们将使用三维直接激光方法来制作负期望结构的3D聚合物支架，然后我们将使用电子束诱导沉积在聚合物支架上沉积母体材料(钨、铁或碳)。然后，我们通过感应耦合氧等离子体去除聚合物，最后根据材料的不同，使用热蒸发、电子束诱导沉积或化学气相沉积的母体材料填充支架。这种方法使我们能够生产具有所需几何形状的微机械测试片，其精度至少比FIB铣削高一个数量级。这对于制造包含裂纹的试件尤其重要，因为在使用部件中出现的自然裂纹(例如，由于腐蚀)非常尖锐，很难使用FIB铣削复制。我们将用X射线纳米层析成像技术研究我们的微米级试件中纳米级裂纹的断裂行为。使用X射线纳米层析成像将使我们能够实时观察裂纹与周围微观结构的相互作用。微断裂测试获得的信息将验证我们的元胞自动机有限元模型，然后我们使用该模型将结果外推到宏观组件。如果成功，我们将在未来对纳米添加制造的试件进行中子辐照，以研究辐射损伤对复杂几何组件结构完整性的影响。高剂量辐照的复杂几何样品对聚变核电站很重要，因为许多结构部件的几何形状复杂，并由物理决定。因此，在后续研究中，我们将与库勒姆聚变能源中心、国家核实验室和核先进制造研究中心合作。

We need to know the behaviour of novel materials in the presence of high irradiation and high temperature before we could embark on building advanced Generation IV and fusion nuclear systems. However, health and safety issues prevent us from testing macromechanical irradiated coupons in the laboratory. The solution is to test very small volumes of irradiated material, i.e. micromechanical coupons, and use multi-scale modelling to extrapolate the measured behaviour to macromechanical components. Because of their very low volume such specimens can be lab tested, even when irradiated to low or medium level of activity. This offers a possibility of testing multiple specimens to investigate stochastic effects, e.g. effects of irradiation on the shift of the ductile to brittle transition. The manufacturing technology is fast moving from subtractive methods to additive methods. Additive manufacturing can produce geometries which so far have not been possible using the traditional subtraction (e.g. milling) methods. The advances of additive manufacturing, so far, have not been replicated in micromechanical testing. Currently the common method for fabricating micromechanical coupons is to use Gallium or Helium Focused Ion Beam (FIB) micro-milling. In FIB milling, charged ions of helium or gallium are focused on the sample, sputtering the parent material in a pre-defined geometry until the desired shape is milled. The subtractive FIB milling method not only is not representative of additive manufacturing foreseen to be used in future nuclear complete fabrication, it leaves damages such as helium bubbles or gallium implantation in the milled micromechanical samples. It is therefore highly desirable to develop a new method to fabricate micro-scale micromechanical testing coupons that do not suffer from FIB damage (i.e. helium or gallium implantation or in severe cases, parent material amorphisation).In this feasibility study, we will investigate the applicability of a novel nano-additive manufacturing methodology, originally developed for tuneable optical systems, to fabricate micromechanical specimens. We will be using three-dimensional direct laser method to produce a 3D polymer scaffolding of the negative desired structure, we will then deposit the parent material (tungsten, iron or carbon) on the polymer scaffolding using electron beam induced deposition. We then remove the polymer by inductively coupled oxygen plasma, and finally fill out the scaffolding with parent material using thermal evaporation, electron beam induced deposition or chemical vapour deposition depending on the material. This method allows us to produce a micromechanical test coupon with desired geometry with an accuracy of at least one order of magnitude better than FIB milling. This is especially important for fabricating specimens that contain cracks as the natural cracks occurring in service components, for example due to corrosion, are very sharp which are hard to replicate using FIB milling. We will investigate the fracture behaviour of nanometre cracks in our micro-scale specimens by X-ray nano-tomography. Using X-ray nano-tomography will allow us to observe, in real time, the interaction of the crack with the surrounding microstructure. The information obtained from micro-fracture tests will validate our cellular automata finite element model which we then use to extrapolate the results to a macro-scale component.If successful, in future we will neutron irradiate the nano-additively manufactured specimens to investigate the effects of irradiation damage on the structural integrity of components with complex geometries. Complex geometry specimens irradiated with a high dose are important for fusion plants as the geometry of many structural components is complex and dictated by physics. Thus in the follow-on research we will be working with Culham Centre for Fusion Energy, National Nuclear Laboratory and Nuclear Advanced Manufacturing Research Centre.