Collaborative Research: Far-from-equilibrium surfaces of high entropy alloys: interplay between frictional sliding and corrosion damage

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Non-Technical SummaryMulti-principal-element alloys, also known as high entropy alloys (HEAs), are an emerging class of metallic materials which often consist of five or more alloying elements with similar concentration. HEAs have generated considerable interest as potential structural materials for use under harsh conditions due to their superior mechanical properties and chemical stability compared to traditional alloys. Despite all of the promise that HEAs hold, little is known about their surface structure and properties upon simultaneous mechanical impacts and chemical reactions under harsh environments. This collaborative research between Virginia Tech and the University of Alabama aims to develop a scientific understanding of the structure and formation mechanism of the surface of HEAs after simultaneous wear and rusting (i.e. tribocorrosion) in chloride-containing aqueous solution (e.g. seawater). By combining advanced surface characterization tools and multi-scale computer simulations, the link between surface defects, deformation, and tribocorrosion susceptibility of HEAs will be established. This project will lead to the design of metals with high tribocorrosion resistance for critical applications which require high wear and rust resistance under harsh conditions. The highly cross-disciplinary research activities will provide graduate students with diverse training in materials science, tribology, corrosion, and computational materials science, as well as the collaborative teamwork experience. It will also positively impact several education and outreach initiatives, especially the involvement of underrepresented groups via research opportunities at Virginia Tech and the University of Alabama.Technical SummaryOur current understanding of the tribocorrosion mechanisms of HEAs is mainly challenged by a lack of understanding of the selective dissolution/oxidation of principal elements, as well as the new deformation physics at/below the surface. The synergy between mechanical and chemical attack drastically alters the materials’ surface condition and corrosion susceptibility, especially for Cr-containing HEAs that rely on a thin yet protective surface oxide layer (i.e. passive layer) for corrosion protection in air and water. This project will combine advanced surface characterization and multi-scale simulations to reveal how frictional sliding-induced depassivation leads to the formation of far-from-equilibrium microstructure and composition at the surface, and the influence of the surface electrochemistry and mechancis that act synergistically on the overall repassivation kinetics and tribocorrosion rate. Specifically, the PIs will (1) determine how alloy concentration and grain size affect wear, corrosion, and their synergy, (2) elucidate the chemistry, composition, and defect characteristics of the tribocorroded surface structure and its formation mechanism, (3) understand wear-induced defect generation and microstructure evolution using atomistic simulations, and (4) develop an experimentally validated, predictive model for tribocorrosion using multiphysics simulations that incorporate rate-limiting corrosion and repassivation steps. The integrated experimental and computational approach has great potential to reduce the materials creation and deployment cycle to fabricate tribocorrosion-resistant alloys over a larger design space than traditionally known. Research opportunities and mentorship programs will be created at Virginia Tech and the University of Alabama for undergraduate students, especially for women (with both PIs serving as role models) and under-represented minorities. In addition, the proposed outreach activities will positively impact local K-12 students and the broad internet audience to promote their interest and enhance their knowledge in STEM fields.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.