Ion irradiations of fusion reactor materials

为了优化材料在聚变环境中的操作，我们需要对其机械性能和辐照引起的机械性能变化进行机械理解。牛津大学正在进行的一个项目集中在发展对未辐照材料的机械特性的理解，并研究在50-100keV重离子照射下薄电子显微镜样品的辐射损伤演变。使用变薄的试样存在困难，因为缺陷相对容易从试样的自由表面逸出；观察到的损伤可能不是典型的由材料深处中子辐照引发的级联所引起的损伤。因此，我们现在需要研究用MeV重离子辐照的材料。使用萨里大学设备进行此类研究的可行性已在铁铁合金的试验中得到证实。我们的第一个显微实验显示了高密度的可分解位错环，在质量上类似于在中子辐照的铁铁合金中看到的微观结构。我们现在需要进行一套系统的辐照实验，我们将对更广泛的材料进行辐照，并研究由此产生的辐射损伤及其对机械性能的影响。我们将包括Fe， FeCr（高达12% Cr）， RAFM和ODS钢的TEM和微束试样。实验还将扩展到在Fe+辐照前立即预先注入He+的材料，以模拟嬗变气体的影响。透射电镜将研究每种材料的辐照损伤、损伤后和变形位错结构，包括变形前和变形后从微梁上切割的样品。目的是使用全范围的TEM技术，包括标准衍射对比和高分辨率方法以及M.L. Jenkins及其同事开发的新技术，对位错、位错环和空隙进行完整的微观结构表征。先进的分析技术将用于研究局部化学，例如在ODS粒子的界面上。微梁将用于研究辐照材料的弹性、塑性和断裂行为。我们将通过在单个晶粒内切割样品来研究材料的体积特性。晶界偏析和脆化将作为晶界晶体学、局部化学和辐射损伤的函数来研究。滑移通过边界的传输将通过加载包含边界和压痕作为局部位错源的微梁来研究。边界的断裂强度将通过弯曲试样内的边界缺口来研究。

To optimise materials for operation in a fusion environment, we need to develop a mechanistic understanding of their mechanical properties and of the changes in mechanical properties induced by irradiation. An ongoing project at Oxford has concentrated on developing an understanding of the mechanical properties of unirradiated materials and on studies of the evolution of radiation damage in thin electron microscope specimens by 50-100keV heavy-ion irradiation. There are difficulties with using thinned specimens, in that defects can relatively easily escape from the free surfaces of the specimens; the damage observed may not be typical of that introduced by cascades initiated by neutron irradiation deep within a material. Hence we now need to study materials irradiated with MeV heavy ions in the bulk.The feasibility of using the Surrey University facility for such studies has been demonstrated in a trial implantation of FeCr alloys. Our first microscopy experiments have shown a high density of resolvable dislocation loops, qualitatively similar to the microstructures seen in neutron-irradiated FeCr alloys. We now need to carry out a set of systematic irradiation experiments, where we will irradiate a wider range of materials, and study the resultant radiation damage and its effects on mechanical properties. We will include both TEM and microbeam specimens of Fe, FeCr (up to 12% Cr), RAFM and ODS steels. The experiments will also be extended to materials pre-implanted with He+ immediately before Fe+ irradiation, so as to simulate the effects of transmutation gases. Transmission electron microscopy will be used to study irradiation damage and post-damage and deformation dislocation structures in each of the materials, including specimens cut from the microbeams before and after deformation. The aim will be a complete microstructural characterisation of dislocations, dislocation loops and voids using a full range of TEM techniques, including both standard diffraction-contrast and high-resolution methods and novel techniques developed by M.L. Jenkins and co-workers. Advanced analytical techniques will be used to study local chemistry, for example at the interfaces of ODS particles. Micro-beams will be used to study the elastic, plastic and fracture behaviour of irradiated materials. We will study the bulk properties of the materials, by cutting specimens within single grains. Grain boundary segregation and embrittlement will be studied as a function of grain boundary crystallography, local chemistry and radiation damage. Slip transmission through boundaries will be studied by loading of microbeams containing a boundary and an indentation as a local dislocation source. Fracture strength of boundaries will be studied by notching of boundaries within bend specimens.