CAREER: Characterization and understanding of point defect evolution during corrosion-induced grain boundary migration

金属和合金暴露在环境中会生锈和降解。工程材料的生锈和退化问题引起了人们对可靠性的关注，并带来了巨大的缓解成本。生锈不可避免地涉及到材料内部微观缺陷的演变。典型的缺陷包括晶界、位错和点（原子级）缺陷，例如空原子位置。缺陷的特征，如缺陷的类型、位置和密度，可以显著影响工程合金的性能。了解当材料生锈时缺陷是如何产生和相互作用的，是有效解决这些退化问题的关键步骤。虽然研究人员现在可以在材料中以高分辨率探测纳米和更大尺寸的晶界和位错，但原子级点缺陷的成像，如缺失的原子或空位，仍然是一个关键的挑战。这限制了腐蚀科学以及催化和电池等其他领域的基础发现。本研究项目旨在利用PI开发的一种新的原子级点缺陷成像技术来阐明合金生锈时点缺陷和晶界之间的相互作用。本研究有助于对工程系统和基础设施的锈蚀失效进行预测，以防止锈蚀事故的发生。此外，对锈蚀过程中晶界迁移运动的科学理解推动了工程方法的发展，为先进的能源系统、运输和国防应用制造低成本、高性能和抗损伤的合金。教育和推广活动包括与“女生物理”夏季研讨会的合作，该研讨会为州立大学地区的初高中女生提供了一个亲身实践的、身临其境的、有趣的物理介绍。这些活动将研究与多层次的教育计划结合起来，培养学生对科学和工程的兴趣，激励学生有效地应对关键的全球挑战，并增加未被充分代表的少数民族对科学和工程的参与。材料的工程晶界（GB）可以显著提高材料的力学、电学、热学等性能。然而，在加热、机械变形和辐射损伤等外界刺激下，gb会发生迁移。因此，利用GB工程取决于在应用相关环境中与GB相关的微观结构的稳定性。虽然热或机械刺激对GB运动的影响已经被广泛研究，但直到最近几年，腐蚀引起的GB迁移才被表征出来。目前，腐蚀诱导的GB迁移对材料腐蚀/损伤容限的潜在机制和影响尚不清楚。关键的知识缺口在于腐蚀产生的多余空位如何与GB运动和应力腐蚀开裂（SCC）过程相互作用。这个问题的解决目前受到纳米尺度上空位分布成像困难的限制。在这里，PI集成了相关的电子显微镜和先进的计算模型来解决这一挑战。该项目旨在：(i)开发一种强大的纳米分辨率空位映射方法，以可视化GB附近的多余空位分布；（ii）从基本缺陷演变的角度揭示腐蚀过程中GB迁移的主要机制。与此同时，多层次的教育和推广计划包括：(1)与“女生物理”暑期工作坊合作，为高中女生举办客座讲座和大学实验室参观，旨在帮助她们克服对女生在STEM领域的刻板印象；(2)开设关于极端环境下材料降解的大学新课程，培养学生应对材料降解挑战的动力。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 SummaryMetals and alloys rust and degrade when exposed to the environment. The problem of engineered materials rusting and degrading has led to crucial reliability concerns with tremendous mitigation costs. Rust inevitably involves the evolution of microscopic defects within the material. Typical defects include grain boundaries, dislocations, and point (atomic level) defects, such as a vacant atomic site. The characteristics of defects, such as their types, locations, and densities, can significantly impact the performance of engineered alloys. Understanding how defects are generated and interact with each other when the material rusts is a critical step to address these degradation problems effectively. While researchers can now probe nanometers and larger sized grain boundaries and dislocations in materials at high resolution, imaging of atomic-level point defects, such as a missing atom or vacancy, remains a critical challenge. This has limited the fundamental discoveries in corrosion science and other fields such as catalysis and batteries. This research program aims to utilize a new atomic-level point defect imaging technique the PI developed to elucidate the interaction between point defects and grain boundaries while the alloys rust. This research facilitates the prediction of failure due to rust in engineering systems and infrastructures to help prevent rust-induced accidents. Also, the scientific understanding of the motion of grain boundaries migration during rusting advances engineering methods to make low-cost, high-performance, and damage-resistant alloys for advanced energy systems, transportation, and defense applications. Education and outreach activities include a partnership with the “Physics for Girls” summer workshop that offers a hands-on, immersive, and fun introduction to physics for girls in middle/high school in the State College area. These activities integrate research with a multi-level educational program, which foster students’ interest in science and engineering, motivate students to effectively address critical global challenges, and increase under-represented minorities involvement in science and engineering. Technical SummaryEngineering grain boundary (GB) in materials can significantly enhance materials’ performance, including mechanical, electrical, and thermal properties, etc. However, GBs will migrate under the influence of external stimuli, such as heating, mechanical deformation, and radiation damage. Thus, taking advantage of GB engineering hinges upon the stability of GB-related microstructure in application-relevant environments. While the effect of thermal or mechanical stimuli on GB motion has been vastly studied, it was only until recent years that corrosion-induced GB migration was characterized. Currently, the underlying mechanism and the impact of corrosion-induced GB migration on the corrosion/damage tolerance of materials remain elusive. The critical knowledge gap resides in how excess vacancies generated by corrosion interact with GB motion and the stress corrosion cracking (SCC) process. Resolving this question is currently limited by the difficulty of imaging vacancy distribution at the nanoscale. Here, the PI integrates correlative electron microscopy and advanced computational modeling to address this challenge. This project aims to: (i) develop a robust nanometer-resolution vacancy mapping method to visualize the excess vacancy distributions near GBs, and (ii) uncover the dominant mechanisms responsible for the GB migration during corrosion from a fundamental defect evolution perspective. Meanwhile, a multi-level education and outreach plan includes: (1) collaborating with the “Physics for Girls” summer workshop by organizing guest lectures and offering university-lab tours to high/middle school girls, aiming to help them overcome the stereotype about girls in STEM; (2) offering a new university course about the degradation of materials under extreme environment to foster students’ motivation in addressing the challenges of materials degradation.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.