Understanding Radiation Induced Transmutation in Tungsten Alloys for Nuclear Fusion

可行的核聚变发电厂的发展依赖于能够承受高中子辐射和聚变等离子体周围极端环境中高温的综合影响的材料。用于面向等离子体组件的材料很少能够满足这些要求。钼、碳复合材料和铍都已被检查，但所有这些都存在活化、氚保留或溅射率的问题。钨现在被认为是偏滤器的主要候选材料，可能是所有第一壁装甲。在14 MeV中子辐照期间，嬗变效应将改变任何材料的成分，使寿命评估的准确预测进一步复杂化。先前的工作已经表明，二元钨-钽和钨-钽合金在辐照暴露下可以形成纳米尺寸的沉淀物，其硬化然后最终使材料脆化。然而，三元W-Re-Ta和W-Re-Os合金在辐照下表现出完全不同的行为，这提出了关于使用预合金材料模拟嬗变途径的最佳途径的重要问题，以及关于辐照和未辐照合金中沉淀形成机制的基本问题。此外，还没有研究钨-钽-锇合金，尽管这是终端组成，以前的研究只集中在二元系统，有时溶质含量过高。这可能会导致观察到在操作条件下预期不到的沉淀物。在该项目中，代表更精确嬗变产物的高阶（来自钨-钽-锇系统的三元和四元合金）合金将暴露于重离子辐照，然后使用原子探针断层扫描，TEM和纳米压痕测量的多技术方法进行检查，旨在将原子尺度的3D化学信息与这些合金的机械性能联系起来。特别是如何热稳定这些集群将使用热老化处理研究。尚未就此对该系统进行研究，这将是首次观察到溶解或生长。纳米压痕将用于研究位错与簇的相互作用以及这如何导致硬化。这些实验的关键是了解，如果热处理可以用来延长偏滤器的寿命在服务中退火的辐射damage.In这种方式，我们希望获得更深入的了解这些材料中的溶质添加剂之间的相互作用后照射，更好地了解动力学和热力学的辐射辅助沉淀，以及如何改变机械行为。这将为CCFE进行的原子模拟提供有价值的数据，并最终为偏滤器提供更好的寿命预测。

The development of viable nuclear fusion power plants relies on materials capable of withstanding the combined effects of high neutron irradiation and elevated temperatures in an extreme environment around the fusion plasma. Few materials proposed for plasma-facing components are capable of meeting these demands. Molybdenum, carbon composites and beryllium have all been examined but issues with either activation, tritium retention or sputtering rate exist for all these. Tungsten is now considered the leading candidate for the divertor and possibly all first wall armour. During irradiation with 14MeV neutrons, transmutation effects will alter the composition of any materials, further complicating accurate predictions of lifetime assessment. Previous work has shown that binary tungsten -rhenium and tungsten -tantalum alloys can form nanosized precipitates under irradiative exposures, which harden then ultimately embrittle the materials. However ternary W-Re-Ta and W-Re-Os alloys have been shown to behaviour quite differently under irradiation which raises important questions about the best route for mimicking transmutation pathways using pre-alloyed materials and fundamental questions regarding the mechanisms of precipitation formation in both irradiated and unirradiated alloys. In addition there have been no studies of tungsten-rhenium-tantalum-osmium alloys despite this being the terminal composition, previous studies focused on binary systems only and sometimes with overly high solute contents. This can lead to precipitates being observed that are not expected under operational conditions. In this project, higher-order (both ternary and quaternary alloys from the of tungsten-rhenium-tantalum-osmium systems) alloys representing more accurate transmutation products will be exposed to heavy ion-irradiation, then examined using a multi-technique approach of Atom Probe Tomography, TEM and Nanoindentation Measurements, aiming to link 3D chemical information at the atomic-scale to mechanical properties of these alloys. In particular how thermally stable these clusters are will be studied using thermal aging treatments. There has been no studies performed on this system with respect to this and this will be the first time the dissolution or growth will be observed. Nanoindentation will be used to study the interaction of dislocations with clusters and how this lead to hardening. These experiments are key to understanding if thermal treatments can be used to prolong divertor lifetime in service by annealing out radiation damage.In this manner we hope to obtain a much deeper understanding of interactions between solute additions in these materials following irradiation, better understand the kinetics and thermodynamics of irradiation assisted precipitation and how this alters the mechanical behaviour. This will provide valuable data needed to underpin atomistic simulations being performed at CCFE and eventually lead to better lifeing predictions for the divertor.EPSRC research theme is Energy.