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

非技术总结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，包括高效的核能生产和空间探索。高熵合金(HEAs)是一种很有前途的高强度和抗辐射材料，因为HEAs含有许多元素的混合物，这些元素扰乱了化学秩序。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化的基本了解。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，以及化学无序是如何干扰和阻止这一不良过程的。开发高抗辐射、高强度和高稳定性的最佳合金需要这样的见解，这些合金不仅能够实现高效率、低碳或零碳排放的新的先进发电技术，而且更广泛地说，可以改变许多与能源和空间相关的技术领域。从事该项目的学生将对材料的化学和物理以及固体中的缺陷有深入的了解，并在材料科学的重要技术方面获得经验。为参与该项目的研究生提供国际学生交流和国内实习机会。在整个项目期间，向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群体的参与。高熵合金(HEAs)由于其独特的电子结构，具有优异的力学性能和较高的抗辐射能力，是一类非常优秀的材料。这些合金中的化学无序和成分波动对能量耗散和对辐射的响应有很大的影响。虽然以前的透射电子显微镜和其他研究表明，化学无序度的增加抑制了损伤的积累，但他们无法发现2 nm以下的空位团，这为理解这些合金中缺陷的形成和堆积留下了关键的空白。这项研究旨在通过结合原位和非原位正电子湮没谱(PAS)和原位和非原位电子显微镜捕捉孤立的空位、小空位团簇、较大的团簇和空穴来实验监测原子尺度上的缺陷形成及其向大团簇和空穴的堆积，从而弥合辐射诱导缺陷的原子尺度和介观尺度之间的差距。结合离子辐照的原位PAS和原位TEM测量，提供了原子尺度(PAS)和介观尺度(TEM)的缺陷动力学图像，包括产生、湮灭和演化。这项拟议的研究有望揭示辐射环境中化学无序对缺陷形成、迁移和演化的影响，并通过对化学复杂性从1到5的合金中原子和介观水平上的碰撞级联缺陷产生的研究，揭示单相浓缩固溶体合金(SP-CSA)和HEAs中的损伤和退火机制。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.