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

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关键挑战。目前的解决办法往往依赖昂贵和稀缺的元素，这突出表明需要更可持续的替代品。这项研究提出了一类新的复杂集中的合金（CCA），利用本地化学有序（LCO），以提高损伤容限，而不依赖于这些关键元素的发展，特别是在低温下。LCO是指金属固溶体中原子对或原子簇的重复构型。它可以有目的地影响变形机制，而不会产生清晰的界面，这是常见的裂纹部位。通过战略性地利用不同类型的LCO，该提案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。该研究将采用综合实验和计算方法来开发用LCO增强的CCA。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，这可能是在各种应用中增韧材料的新机制。这项工作的更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外联工作，特别是来自代表性不足的社区，在可持续合金设计领域培养下一代创新者。技术总结本研究计划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的性能，特别是在低温下。这种方法的核心是利用局部化学有序（LCO）诱导表现出负的本征堆垛层错能（SFE）的合金内的故障塑性机制。层错-马氏体的最小组分-提供了具有最小应变局部化的理论上最优的细化结构。因此，断层塑性可以提供强度，延展性和韧性的改善，特别是在低温下。该提案解决了实现断层塑性的固有挑战，其中所需的低或负SFE同时促进马氏体相变，通过考虑LCO的影响。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机械影响材料性能。这一建议的智力价值在于它的潜力，探索和利用亚稳态和LCO在fcc CCAs在低温环境中增强鲁棒性。这一奖项反映了NSF的法定使命，并已被认为是值得通过评估使用基金会的智力价值和更广泛的影响审查标准的支持。

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.