CAREER: Resolving the origins of microgalvanic corrosion on metal surfaces

腐蚀(锈蚀)是一个古老的冶金问题，其潜在的机理至今仍未被很好地了解。这项研究计划的目的是通过使用最先进的仪器，在纳米尺度上看到金属在液体中的锈蚀，从而揭示这些隐藏的机制，并充分了解铁锈。通过了解材料与其环境之间的复杂相互作用，变革性的成果包括预测和评估腐蚀的先验方法，以及使工程师能够设计出具有优异耐腐蚀性的材料的基本框架。能够控制锈蚀具有深远的影响，从使超轻合金设计能够用于航空航天应用，到关键基础设施的材料，如发电、交通、通信、国防以及水和废物处理设施。通过培养下一代腐蚀工程师，综合教育计划扩大了这项研究的影响。教育活动将使从高中到研究生院的学生受益，同时为服务不足的学生和少数族裔学生提供机会，为解决具有国家意义的问题作出贡献。技术概述工程师设计和加工大多数工程合金以析出第二相；在这些相强化合金的同时，它们也是引发腐蚀的热力学驱动力。通过选择合金成分和加工路线来优化基本的电化学性能，可以定制固有的耐腐蚀性，但适当的成分和加工路线仅适用于选定的材料体系，并且仅在特定的环境条件下执行。如何从这些系统扩展到其他材料和环境，仍然是一个乏味的反复试验过程。为了解决这一局限，并推进设计具有优异腐蚀性能所需的基础科学，本研究通过将最先进的扫描开尔文探针力显微镜(SKPFM)和扫描电化学显微镜(SECM)与第一性原理电子性质模拟相结合，将镁锂(Mg-Li)合金在溶液中的电极电位与其电子结构联系起来。利用SKPFM测量伏尔塔势(一种表面电子性质)，通过功函数提供了跨越原子结构和宏观电化学性质的实验联系。作为补充，SECM量化了腐蚀过程中的表面反应动力学。总之，这项研究为将局部成分和结构与电化学性质--一个控制材料使用寿命的关键因素--联系起来提供了一个新的理论框架。这一奖项反映了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 SummaryCorrosion (rust) is an age-old metallurgical problem whose underlying mechanisms are still not well-understood. The purpose of this research program is to uncover these hidden mechanisms and fully understand rust by using state-of-the-art instruments that allow us to see metals rust in liquids at the nanometer scale. By understanding the complex interplay between a material and its environment, transformative outcomes include an a priori approach for predicting and assessing corrosion, and a fundamental framework enabling engineers to design materials with superior corrosion resistance. Being able to control rust has far-reaching implications, from enabling ultra-light alloy design for aerospace applications, to materials for critical infrastructure, such as power generation, transportation, communications, defense, and water and waste treatment facilities. An integrated education plan extends the impact of this research by educating the next generation of corrosion engineers. Educational activities will benefit students from high school to graduate school, while providing opportunities for underserved and minority students to contribute to solving problems of national significance. Technical SummaryEngineers design and process most engineering alloys to precipitate secondary phases; while these phases strengthen the alloy, they also act as the thermodynamic driving force for corrosion initiation. Inherent corrosion resistance can be tailored by selecting alloy constituents and processing routes to optimize fundamental electrochemical properties, but the appropriate constituents and processing routes are known only for select material systems and perform only under specific environmental conditions. How to expand beyond these systems to other materials and environments is still a tedious trial-and-error process. To address this limitation and advance the fundamental science needed to design for superior corrosion performance, this research connects the electrode potential of magnesium-lithium (Mg-Li) alloys in solution to their electronic structure by integrating state-of-the-art scanning Kelvin probe force microscopy (SKPFM) and scanning electrochemical microscopy (SECM) with first principles electronic property simulations. Using SKPFM to measure Volta potential (a surface electronic property) provides an experimental link spanning atomic structure and macroscale electrochemical properties via the work function. In complement, SECM quantifies the surface reaction kinetics during corrosion. Altogether, this research provides a new theoretical framework for relating local composition and structure to electrochemical properties--a critical factor governing material operational lifetimes.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.