Alloy design and high-temperature mechanics of plasma-facing materials

钨由于其熔点（3420 ℃），溅射率低，以及良好的高温强度和导热性而成为聚变反应堆的主要等离子体表面材料。不幸的是，钨是脆性的性质和它的韧脆转变温度增加中子照射下，由于形成晶格缺陷，如位错和空隙。关于W基二元合金的有限数据表明，Ti、V或Ta等合金元素可提高材料的延展性。不幸的是，迄今为止，合金的选择都是通过试错来完成的，而现有的关于辐照钨合金高温力学的数据主要集中在W注入试样的纳米压痕研究上。本项目的目的是通过采用预先系统的设计方法，使用热力学和从头计算，耦合在相关的密度泛函理论和蒙特卡罗模拟相稳定性照射下。最有前途的合金将通过粉末冶金生产，并在曼彻斯特使用分析电子显微镜进行深入表征，包括具有原子分辨率的Titan ChemiSTEM显微镜。可靠预测反应堆内合金性能的关键是原位监测高温（<1000 ℃）下的损伤形成和塑性变形机制。前者将通过使用离子辐照结合透射电子显微镜来完成，以便原位可视化原子迁移，局部化学偏析以及晶格缺陷成核和演化作为损伤水平和温度的函数。塑性变形机制将通过在高亮度同步加速器设施上进行现场机械测试来进行真实的实时监测。他们的实验能力只允许在最近几天重建散装多晶粒结构在真实的时间作为可塑性的演变。这些结果是这些天非常需要在核聚变技术社区验证和指示多尺度建模活动，因此，预计将支持安全案例和指导合金设计策略的DEMO和未来的商业聚变发电厂。

Tungsten stands as the main plasma-facing material for fusion reactors due to its melting point (3420C), low sputtering yield, and good high-temperature strength and thermal conductivity. Unfortunately, tungsten is brittle by nature and its ductile-to-brittle transition temperature increases under neutron irradiation, due to the formation of lattice defects such as dislocations and voids. The limited data available on W-based binary alloys reveals that alloying elements such as Ti, V or Ta improves the material's ductility. Unfortunately, alloy selection has to date been done by trial-and-error, and the existing data on high-temperature mechanics of irradiated tungsten alloys reduces mainly to nano-indentation studies in W-implanted specimens.The aim of this project is to accelerate the development of the next generation of binary and ternary W alloys, by adopting upfront a systematic design approach using thermodynamic and ab initio calculations, coupled where relevant with density functional theory and Monte Carlo simulations of the phase stability under irradiation. The most promising alloys will be produced by powder metallurgy, and characterised in-depth using analytical electron microscopy in Manchester, including the Titan ChemiSTEM microscope with atomic resolution. The key to reliable predictions of in-reactor alloy performance is to monitor in situ the damage formation and the plastic deformation mechanisms at elevated temperatures (<1000C). The former will be done by using ion irradiation in combination with a transmission electron microscope, in order to visualise in situ the atomic migration, local chemical segregations, and the lattice defect nucleation & evolution as a function of damage level and temperature. The plastic deformation mechanisms will be monitored in real time by performing in situ mechanical testing at high-brilliance synchrotron facilities. Their experimental capabilities allow only in very recent days to reconstruct the bulk multi-grain structure in real time as plasticity evolves. These results are these days in very much need to validate and dictate multiscale modelling campaigns in the nuclear fusion technology community, and are therefore expected to support safety cases and steer alloy design strategies for DEMO and future commercial fusion power plants.