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包括高效核能生产和空间探索在内的许多技术应用至关重要。高熵合金（HEAs）是一种有前途的高强度和抗辐射材料，因为它含有许多破坏化学秩序的元素的混合物。本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是如何演变的，以及化学紊乱是如何干扰和停止这一不良过程的。开发具有高抗辐射性、高强度和高稳定性的最佳合金需要这样的见解，这不仅可以实现高效率、低碳或零碳排放的新型先进发电技术，而且更广泛地说，可以改变与能源和空间相关的许多技术领域。参与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，并获得材料科学中重要技术的经验。为参与项目的研究生提供国际交换生和国内实习机会。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展活动，积极鼓励代表性不足的群体参与。高熵合金（HEAs）由于其独特的电子结构而具有优异的机械性能和高辐射耐受性，正成为一类杰出的材料。这些合金的化学无序性和成分波动对其能量耗散和辐照响应有很大影响。虽然之前的透射电子显微镜（TEM）和其他研究表明，增加化学无序性可以抑制损伤的积累，但它们无法揭示2 nm以下的空位团簇，这对理解这些合金中的缺陷形成和积累留下了关键的空白。本研究旨在通过原位和非原位正电子湮灭光谱（PAS）与原位和非原位TEM相结合，在原子尺度上监测缺陷的形成和形成大簇和空隙，以捕获孤立的空位、小的空位团和大的簇和空隙，从而弥补原子尺度和中尺度之间的差距。原位PAS和原位TEM测量与离子辐照相结合，可以在原子尺度（PAS）和中尺度（TEM）上提供缺陷动力学的图像，包括产生，湮灭和演变。该研究旨在揭示化学无序对辐射环境中缺陷形成、迁移和演化的影响，并通过在原子和中尺度水平上研究从一种化学成分增加到五种化学成分的合金中碰撞级联产生的缺陷，揭示单相集中固溶体合金（SP-CSAs）和HEAs的损伤和退火机制。该奖项反映了美国国家科学基金会的法定使命，并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，被认为值得支持。

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.