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

多主元素合金，又称高熵合金（HEAs），是一类新兴的金属材料，通常由五种或五种以上浓度相近的合金元素组成。与传统合金相比，HEAs具有优越的机械性能和化学稳定性，因此作为在恶劣条件下使用的潜在结构材料引起了相当大的兴趣。尽管HEAs具有很大的潜力，但人们对其在恶劣环境下同时发生机械冲击和化学反应时的表面结构和性能知之甚少。弗吉尼亚理工大学和阿拉巴马大学的这项合作研究旨在科学地了解HEAs在含氯水溶液（如海水）中同时磨损和生锈（即摩擦腐蚀）后表面的结构和形成机制。通过结合先进的表面表征工具和多尺度计算机模拟，将建立HEAs表面缺陷、变形和摩擦腐蚀敏感性之间的联系。该项目将为苛刻条件下需要高耐磨性和防锈性的关键应用设计具有高耐摩擦腐蚀性的金属。高度跨学科的研究活动将为研究生提供材料科学，摩擦学，腐蚀和计算材料科学方面的多样化培训，以及合作团队的经验。它还将对一些教育和推广活动产生积极影响，特别是通过弗吉尼亚理工大学和阿拉巴马大学的研究机会，让代表性不足的群体参与进来。你目前对HEAs摩擦腐蚀机制的理解主要是由于缺乏对主要元素的选择性溶解/氧化以及表面/表面以下的新变形物理的理解而受到挑战。机械和化学腐蚀之间的协同作用极大地改变了材料的表面状况和腐蚀敏感性，特别是对于依靠薄而保护性的表面氧化层（即钝化层）在空气和水中进行腐蚀保护的含cr HEAs。该项目将结合先进的表面表征和多尺度模拟，揭示摩擦滑动诱导的脱钝化如何导致表面形成远离平衡的微观结构和成分，以及表面电化学和机制对整体再钝化动力学和摩擦腐蚀速率的协同作用的影响。具体来说，pi将(1)确定合金浓度和晶粒尺寸如何影响磨损、腐蚀及其协同作用；(2)阐明摩擦腐蚀表面结构的化学、组成和缺陷特征及其形成机制；(3)利用原子模拟了解磨损诱导缺陷的产生和微观结构演变；结合限速腐蚀和再钝化步骤的多物理场模拟摩擦腐蚀预测模型。综合实验和计算方法具有巨大的潜力，可以减少材料的制造和部署周期，在比传统已知的更大的设计空间内制造耐摩擦腐蚀合金。弗吉尼亚理工大学（Virginia Tech）和阿拉巴马大学（University of Alabama）将为本科生创造研究机会和导师项目，尤其是女性（两位pi都是榜样）和代表性不足的少数族裔。此外，建议的外展活动将对本地的K-12学生和广大互联网观众产生积极影响，以提高他们对STEM领域的兴趣和知识。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 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.