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

Non-technical Summary

Metals 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 Summary

Engineering 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.