RII Track-4: Experimentally-informed Mesoscale Modeling of Anisotropic Grain Boundary Solute Segregation in Nanocrystalline Alloys

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Nearly all structural materials are polycrystalline systems; their microstructures are comprised of crystalline grains that are joined at internal interfaces, termed grain boundaries (GBs). Owing to their nanometric grain size, nanocrystalline (NC) metals exhibit unique combinations of properties that are not commonly observed in their coarse-grained counterparts. However, NC metals are susceptible to rapid grain coarsening during processing or under service conditions, which in turn limits their use in many engineering applications, such as structural, energy, and electronics. Recent experimental findings suggest GB solute segregation as a design strategy to manipulate interface properties and develop thermally stable NC metals. Through coordinated experimental and computational studies, the main research objective of this project is to gain fundamental insights into the role of GB geometry in solute segregation and the resultant impact on the thermal stability of NC alloys. The experimental portion of this project will be conducted at the Center for Integrated Nanotechnologies at Sandia National Laboratories (CINT-SNL). This project will uniquely position the PI to be at the forefront of innovative research on nanomaterials, metallurgy and interface physics, and it will serve as a catalyst for future collaborations and partnerships between Clemson University and CINT-SNL. Further, this project provides a fertile avenue to train future generation of engineers and scientists with the interdisciplinary skill set necessary for careers in knowledge-intensive industries in South Carolina, which is an emerging advanced manufacturing hub.While great strides have been recently made towards the use of GB solute segregation to design thermally stable NC metals, our current understanding is still lacking as most existing efforts rely on the isotropy assumption in segregation - solute atoms segregate equally and uniformly to all GBs. This is an overly simplistic assumption as GB properties are greatly influenced by the boundary’s geometry. This project advances the current understanding of interface segregation by elucidating the impact of GB geometry on solute segregation behavior. The experimental thrust of this project will be performed at the Center for Integrated Nanotechnologies at Sandia National Laboratories (CINT-SNL), which will allow the PI to take advantage of a suite of cutting-edge high-resolution microscopy facilities. The PI will use tools, including aberration-corrected scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction at CINT-SNL to conduct in situ high-temperature experiments, detailed tomographic reconstructions of samples, chemical mapping, and orientation imaging microscopy of texture and GB character in NC systems with the goal of characterizing and quantifying GB solute concentration for a wide range of GB types. The PI will perform analysis, employing analytical models of interface adsorption, of the experimental data to obtain segregation energies that serve as input parameters to a recently developed mesoscale model of GB segregation and microstructural evolution in NC alloys. Using the experimentally informed model, we will perform systematic computational studies to elucidate the impact of anisotropic GB solute segregation on grain growth and thermal stability of NC alloys.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.