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

非技术摘要金属和合金暴露在环境中时会生锈和降解。工程材料生锈和降解的问题已经导致了严重的可靠性问题，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，如空位。缺陷的类型、位置和密度等特征会对工程合金的性能产生重大影响。了解缺陷是如何在材料生锈时产生并相互作用的，是有效解决这些降解问题的关键一步。虽然研究人员现在可以高分辨率探测材料中的纳米和更大尺寸的晶界和位错，但原子级点缺陷的成像，如丢失的原子或空位，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性发现。这项研究计划旨在利用PI开发的一种新的原子级点缺陷成像技术来阐明合金锈蚀时点缺陷和晶界之间的相互作用。这项研究有助于预测工程系统和基础设施中生锈导致的故障，以帮助防止生锈引发的事故。此外，对锈蚀过程中晶界迁移运动的科学理解促进了制造用于先进能源系统、交通运输和国防应用的低成本、高性能和抗损伤合金的工程方法。教育和外展活动包括与“女生物理学”暑期讲习班合作，为州立大学地区的初中/高中女生提供身临其境和有趣的物理介绍。这些活动将研究与多层次教育计划相结合，培养学生对科学和工程的兴趣，激励学生有效应对关键的全球挑战，并增加未被充分代表的少数族裔对科学和工程的参与。材料中的工程晶界可以显著提高材料的力学、电学和热学性能等性能。然而，晶界会在外界刺激的影响下迁移，如加热、机械变形和辐射损伤。因此，利用GB工程的关键在于与应用相关的环境中与GB相关的微结构的稳定性。虽然热或机械刺激对GB运动的影响已经被广泛研究，但直到最近几年才表征腐蚀诱导的GB迁移。目前，腐蚀诱导的GB迁移对材料的腐蚀/损伤耐受性的潜在机制和影响仍然不清楚。关键的知识差距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。解决这个问题目前受到在纳米尺度上成像空位分布的困难的限制。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。该项目的目标是：(I)开发一种稳健的纳米分辨率空位映射方法，以可视化GB附近的过剩空位分布，以及(Ii)从基本缺陷演化的角度揭示腐蚀过程中GB迁移的主要机制。与此同时，一个多层次的教育和外展计划包括：(1)通过组织客座讲座和为高中/中学女孩提供大学实验室之旅，与“女孩的物理”暑期工作坊合作，旨在帮助她们克服对STEM女孩的刻板印象；(2)提供一门关于极端环境下材料降解的新大学课程，以培养学生应对材料降解挑战的动力。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 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.