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(HEA)，是一种新兴的金属材料，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具有优异的力学性能和化学稳定性，是一种在恶劣条件下使用的潜在结构材料，引起了人们的极大兴趣。尽管HEAs有很大的希望，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对HEAS在含氯的水溶液(如海水)中同时磨损和生锈(即摩擦腐蚀)后的表面结构和形成机理有一个科学的理解。通过结合先进的表面表征工具和多尺度计算机模拟，将建立表面缺陷、变形和HEA摩擦腐蚀敏感性之间的联系。该项目将为在恶劣条件下要求高耐磨性和耐锈性的关键应用设计具有高摩擦腐蚀性能的金属。这些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，以及协作团队合作经验。这也将对几个教育和外展活动产生积极影响，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不足的群体参与进来。技术摘要我们目前对HEAs摩擦腐蚀机理的理解主要受到缺乏对主要元素的选择性溶解/氧化以及表面上/下的新形变物理的理解的挑战。机械和化学侵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，特别是对于依赖薄而又具有保护性的表面氧化层(即钝化层)来保护空气和水中腐蚀的含铬家用电器。该项目将结合先进的表面表征和多尺度模拟来揭示摩擦滑动诱导的去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理协同作用对整体再钝化动力学和摩擦腐蚀速率的影响。具体地说，PI将(1)确定合金浓度和晶粒度如何影响磨损、腐蚀及其协同作用，(2)阐明摩擦磨损表面结构的化学、成分和缺陷特征及其形成机制，(3)使用原子模拟了解磨损诱导缺陷的产生和组织演变，以及(4)使用包含限速腐蚀和再钝化步骤的多物理模拟开发经实验验证的摩擦腐蚀预测模型。这种集成的实验和计算方法具有极大的潜力，可以缩短材料的创建和部署周期，从而在比传统已知的更大的设计空间内制造抗摩擦腐蚀的合金。弗吉尼亚理工大学和阿拉巴马大学将为本科生创建研究机会和指导计划，特别是针对女性(这两个个人投资者都是榜样)和代表性不足的少数族裔。此外，拟议的外展活动将对当地K-12学生和广大互联网受众产生积极影响，以促进他们对STEM领域的兴趣和增强他们的知识。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.