CAREER: Local Chemical Ordering-Assisted Faulting Plasticity in Complex Concentrated Alloys

解决金属在极端条件下的耐久性限制仍然是该行业面临的关键挑战。目前的解决方案往往依赖于昂贵和稀缺的元素，强调需要更可持续的替代品。本研究提出了一种新型复杂浓缩合金（CCAs）的发展，该合金利用局部化学有序（LCO）来提高损伤容忍度，而不依赖于这些关键元素，特别是在低温下。LCO是指金属固溶体中原子对或团簇的重复构型。它可以有目的地影响变形机制，而不会产生清晰的界面，这是裂缝的常见部位。通过策略性地利用不同类型的LCO，本提案旨在设计出具有独特变形机制的cca，提高强度、延展性和韧性，同时避免传统合金在低温下出现的典型脆化。本研究将采用实验与计算相结合的方法来开发LCO增强的CCAs。该提案将使用原位电子显微镜和先进的表征方法研究变形机制，重点关注低温下的行为，这可能为各种应用中的增韧材料开辟新的机制。这项工作的广泛影响将扩展到可持续金属技术的发展，未来材料科学家的教育，以及激励高中学生和教师的推广工作，特别是来自代表性不足的社区，培养可持续合金设计领域的下一代创新者。本研究计划旨在开发新型面心立方（fcc）复合浓缩合金（CCAs），以提高工程材料在恶劣环境条件下的性能，特别是在低温下的性能。该方法的核心是利用局部化学有序（LCO）来诱导具有负本然层错能（SFE）的合金的断裂塑性机制。层错是马氏体中最小的组成部分，它提供了一种理论上最优的精细化结构，具有最小的应变局部化。因此，断层塑性可以提高强度、延展性和韧性，特别是在低温下。该建议通过考虑LCO的影响，解决了实现断层塑性的固有挑战，其中所需的低或负SFE同时促进马氏体转变。该方法将先进的生产和表征技术与热力学和密度功能理论计算相结合，旨在设计具有LCO效应的cca，以抑制从fcc到hcp、bcc或bct马氏体的转变，并了解断裂塑性如何从机械上影响材料性能。该提案的智力价值在于它有潜力探索和利用fcc CCAs中的亚稳态和LCO，以增强低温环境中的鲁棒性。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 SUMMARYAddressing the limitations of metal durability in extreme conditions remains a critical challenge for the industry. Current solutions often depend on expensive and scarce elements, underscoring the need for more sustainable alternatives. This research proposes the development of a novel class of complex-concentrated alloys (CCAs) that utilize local chemical ordering (LCO) to enhance damage tolerance without the reliance on these critical elements, particularly at cryogenic temperatures. LCO refers to the repetitive configurations of atomic pairs or clusters within metal solid solutions. It can purposefully influence deformation mechanisms without creating clear interfaces, which are common sites for cracks. By strategically harnessing different types of LCO, this proposal aims to design CCAs that exhibit a unique deformation mechanism, enhancing strength, ductility, and toughness while avoiding the typical embrittlement seen in conventional alloys at low temperatures. The research will employ integrated experimental and computational methods to develop CCAs reinforced with LCO. This proposal will investigate the deformation mechanism using in situ electron microscopy and advanced characterization methods, with a focus on behavior at cryogenic temperatures, which could pioneer novel mechanisms for toughening materials across various applications. The broader impacts of this work will extend to the development of sustainable metal technologies, the education of future materials scientists, and the outreach efforts to inspire high school students and teachers, particularly from underrepresented communities, fostering the next generation of innovators in the field of sustainable alloy design.TECHNICAL SUMMARYThis research proposal aims to develop novel classes of face-centered cubic (fcc) complex concentrated alloys (CCAs) to enhance the performance of engineering materials under severe environmental conditions, especially at cryogenic temperatures. Central to this approach is the utilization of local chemical ordering (LCO) to induce a faulting plasticity mechanism within alloys that exhibit negative intrinsic stacking fault energy (SFE). Stacking faults—the smallest components of martensite—provide a theoretically optimal refined structure with minimal strain localization. Therefore, faulting plasticity could offer improvements in strength, ductility, and toughness, particularly at cryogenic temperatures. This proposal addresses the inherent challenges of achieving faulting plasticity, where the low or negative SFE required concurrently promotes martensitic transformation, by considering the effects of LCO. The methodology combines advanced production and characterization techniques with thermodynamic and density-functional theory calculations aimed at designing CCAs with an LCO effect tailored to suppress the transformation from fcc to hcp, bcc, or bct martensite, and to understand how faulting plasticity mechanically influences material properties. The intellectual merit of this proposal lies in its potential to explore and harness metastability and LCO within fcc CCAs for enhanced robustness in cryogenic environments.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.