Role of Diffusion-Induced Grain Boundary Migration in Alloy Oxidation

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NON-TECHNICAL SUMMARYOxidation resistance remains a critical requirement for materials applications at medium to hightemperatures in many key sectors such as energy, transportation, and aerospace. Decades of studies have generated significant knowledge about how to improve the oxidation resistance of structural materials, with strategies including the use of alloying elements, coatings, and surface treatments. However, many of the mechanisms behind these strategies remain elusive limiting our ability to design better performing alloys. In this context, the project addresses the impact of deformation and small grain sizes on the oxidation response of selected structural alloys. The work specifically focuses on elucidating the key role of diffusion along moving grain boundaries supplying elements to the alloy surface to form an oxide layer. This ubiquitous mechanism has been largely ignored and therefore unexplored in the context of alloy oxidation; yet it can explain the impacts of surface deformation and small grain sizes on the oxidation behavior of alloy systems.This program contributes to the general scientific understanding of diffusion along moving grain boundaries as a ubiquitous mechanism in crystalline materials under diffusive conditions and increases our mechanistic understanding of materials under extreme environments with impact on the development of new alloys and microstructures, particularly in the context of advanced manufacturing processes. Because of its focus on materials under extreme environments and specifically high temperature oxidation, the proposed research impacts key areas of industrial and national importance, including transportation, energy, and aerospace. In addition to its scientific and technological impacts, the program also contributes to the recruitment, retention, and training in advanced research methods and techniques of a diverse student body and workforce through its research activities. The project also includes activities and practices focusing on increasing diversity, equity, inclusion, and accessibility awareness in the classroom, laboratories, and campus wide.TECHNICAL SUMMARYOxidation resistance remains a critical requirement for applications at medium to high temperatures in many key sectors (energy, transportation, aerospace). While avenues to improve the oxidation resistance of structural materials, i.e., alloying, coating, and surface treatments, are commonly used, many of the mechanisms behind these strategies remain elusive limiting our ability to design better performing alloys. The project addresses the hypothesis that diffusion-induced grain boundary migration (DIGM) is ubiquitous in alloy oxidation and uniquely explains the impacts of surface deformation and grain refinement on the oxidation behavior of alloy systems. To support this hypothesis, this project uses a series of increasingly complex alloys, from model Ni alloys to multi principal element alloys for which diffusion kinetics have been the object of debate. The program quantifies DIGM during alloy oxidation, generating observations, experimental data, and analyses necessary to increase our understanding of solute transport and phase transformation during DIGM with implications for not only oxidation modeling and mitigation but also for any conventional and complex concentrated alloy under diffusive conditions at intermediate temperatures where DIGM can occur. The approach combines systematic series of experiments using state-of-the-art characterization techniques tying micron scale observations to atomistic mechanisms, establishing the knowledge base for future modeling and computational approaches within the Materials Genome Initiative.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.