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

NON-TECHNICAL SUMMARY Addressing 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 SUMMARY This 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.