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

非技术总结解决极端条件下金属耐久性的局限性仍然是该行业面临的一个严峻挑战。目前的解决方案往往依赖于昂贵和稀缺的要素，这突显了需要更可持续的替代方案。这项研究建议开发一种新型的络合浓缩合金(CCA)，它利用局部化学有序(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指的是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，而界面是裂缝的常见位置。通过战略性地利用不同类型的LCO，该建议旨在设计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。这项研究将采用综合的实验和计算方法来开发LCO增强的CCA。这项建议将利用原位电子显微镜和先进的表征方法来研究变形机制，重点是低温下的行为，这可能是各种应用中增韧材料的新机制的先驱。这项工作的更广泛影响将延伸到可持续金属技术的开发，未来材料科学家的教育，以及激励高中生和教师的外展努力，特别是来自代表不足的社区，培养可持续合金设计领域的下一代创新者。技术总结本研究提案旨在开发新型面心立方(FCC)复杂浓缩合金(CCA)，以提高工程材料在恶劣环境条件下，特别是在低温下的性能。这种方法的核心是利用局域化学有序(LCO)来诱导合金内部呈现负本征层错能(SFE)的断层塑性机制。层错--马氏体中最小的成分--提供了最小应变局部化的理论上最佳的细化组织。因此，断层塑性可以改善强度、延展性和韧性，特别是在低温下。这一建议解决了实现断层塑性的内在挑战，即通过考虑LCO的影响，所需的低SFE或负SFE同时促进马氏体相变。该方法将先进的生产和表征技术与热力学和密度泛函理论计算相结合，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，并了解断层塑性如何从力学上影响材料性能。这项建议的学术价值在于它有潜力探索和利用FCC CCA中的亚稳态和LCO来增强低温环境中的稳定性。这一奖项反映了NSF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.