Collaborative Research: Bridging the atomic scale and the mesoscale in the characterization of defect production and evolution in high entropy alloys

开发能够承受大量辐射和变形的高强度材料对于推进许多技术应用至关重要，包括高效核能生产和太空探索。高熵合金（HEAs）是一种具有高强度和抗辐射性能的新型材料，因为HEAs中含有多种破坏化学有序的元素。这项研究的重点是在原子水平上获得对化学无序的复杂性如何干扰削弱材料的不良缺陷的形成和演变的基本理解。 为了获得这些见解，将使用最先进的分析和成像技术来揭示材料中原子大小的缺陷如何演变以及化学无序如何干扰和阻止这种不受欢迎的过程。 需要这种见解来开发具有高抗辐射性，高强度和高稳定性的最佳合金，这不仅可以实现新的先进发电技术，具有高效率和低或零碳排放，而且更普遍地说，可以改变与能源和空间相关的许多技术领域。从事该项目的学生将深入了解材料的化学和物理以及固体中的缺陷，并获得材料科学重要技术的经验。国际学生交流和国家实习机会提供给参与该项目的研究生。在整个项目期间，为本科生和高中生提供了广泛的研究机会和外联活动，积极鼓励代表性不足的群体参与。技术概述高熵合金（HEAs）由于其优异的机械性能和由于其独特的电子结构而产生的高辐射耐受性而成为一类杰出的材料。这些合金中的化学无序和成分波动对能量耗散和对辐照的响应有很大的影响。虽然以前的透射电子显微镜（TEM）和其他研究表明，损伤积累受到抑制，增加化学无序，他们不能揭示低于2纳米的空位簇，在理解这些合金中的缺陷形成和积累留下关键的差距。 建议的研究旨在实验监测原子尺度上的缺陷形成和它们的积累，以大集群和空洞相结合的原位和非原位正电子湮没光谱（PAS）与原位和非原位TEM捕获孤立的空位，小空位簇，较大的集群和空洞，从而弥合原子尺度和介观尺度之间的差距差距的辐射诱导的HEAs缺陷的表征。原位PAS和原位TEM测量的使用都加上离子辐照提供了一个图片的缺陷动力学，包括生产，湮灭和演变，在原子尺度（PAS）和介观尺度（TEM）。这项拟议中的研究有望揭示化学无序对缺陷形成的影响，研究了单相固溶体合金（SP-CSA）在辐射环境中的迁移和演化，揭示了SP-CSA的损伤和退火机制和HEAs通过研究合金中原子和介观尺度上碰撞级联产生的缺陷，化学复杂性从一到五种成分逐渐增加。该奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估的支持。

NON-TECHNICAL SUMMARYDeveloping high strength materials that can withstand significant amounts of radiation and deformation are critical to advance many technical applications, including efficient nuclear energy production and space exploration. High entropy alloys (HEAs) are emerging as promising high strength and radiation-resistant materials as HEAs contain a mix of many elements that disrupt the chemical ordering. The focus of this research is to gain fundamental understanding at the atomic level on how the complexity of chemical disorder interferes with the formation and evolution of undesirable defects that weakens the material. To gain these insights, state of the art analytical and imaging techniques will be used to reveal how an atomic sized defect in the material evolves and how the chemical disorder interferes and halts this undesirable process. Such insights are needed to develop the optimal alloys with high radiation resistance, high strength and high stability that would not only enable new advanced power generating technologies with high efficiency and low or zero carbon emission but more generally, could transform many technical fields related to energy and space. Students working on the project will develop in-depth understanding on chemistry and physics of materials and defects in solids and gain experience in important techniques in material science. International student exchange and national internship opportunities are offered to the graduate students involved in the project. A wide range of research opportunities and outreach activities are provided to undergraduates and high school students throughout the period of the project where participation of underrepresented groups are actively encouraged. TECHNICAL SUMMARYHigh entropy alloys (HEAs) are emerging as an outstanding class of materials due to their excellent mechanical properties and high radiation tolerance as a result of their unique electronic structure. Chemical disorder and compositional fluctuations in these alloys have large effects on energy dissipation and response to irradiation. While previous transmission electron microscopy (TEM) and other studies showed that damage accumulation was suppressed by increasing chemical disorder, they could not reveal vacancy clusters below 2 nm leaving critical gap in understanding defect formation and buildup in these alloys. The proposed research aims to experimentally monitor defect formation on atomistic scale and their buildup to large clusters and voids by combining in-situ and ex-situ positron annihilation spectroscopy (PAS) with in-situ and ex-situ TEM to capture isolated vacancies, small vacancy clusters, larger clusters and voids, thus bridge the gap between the atomic scale and mesoscale characterization of radiation induced defects in HEAs. The use of In-situ PAS and In-situ TEM measurements both coupled with ion irradiation offers a picture of the defect dynamics including production, annihilation and evolution, on atomic scale (for PAS) and mesoscale (for TEM). The proposed research is expected to reveal the effects of chemical disorder on defect formation, migration and evolution in a radiation environment and reveal the damage and annealing mechanisms in Single -Phase Concentrated Solid Solution alloys (SP-CSAs) and HEAs through the study of defect production from collision cascades on an atomic and mesoscale level in alloys with increasing chemical complexity from one to five constituents.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.