CAREER: Order-induced heterogeneities in the deformation behavior of FCC concentrated solid solutions

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This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).Non-technical SummaryThe realization of new, stronger materials is a critical element to the success of emerging technologies in a diverse set of application areas including civil infrastructure, automotive, and aerospace. For example, the ranges of electric vehicles can be improved with stronger alloys (i.e., mixtures of metals and additives), by enabling lower weight vehicle components without a compromise to passenger safety. One key pathway to improving strength is through an understanding of how alloys deform (i.e., respond to loading). Traditional understanding emphasizes the importance of additive chemistry and concentration in directing deformation. However, this rationale has shortcomings in explaining the behavior of alloys with unusually large concentrations of additives. These concentrated alloys include many technologically important materials such as high strength steels. To address these shortcomings, this research effort explores the following question: How does the atomic-scale organization of additives in concentrated alloys influence how the alloy bends? This question is motivated by the hypothesis that, in addition to chemistry and concentration, the additive organization play an important and under-recognized role in directing bending. To reveal this link, forefront mechanical testing techniques and computational models are developed and used. In addition to advancing tools for materials testing, this effort provides new fundamental insights for how these special class of alloys bend, that provides a foundational understanding to engineer materials with improved strength. More broadly, the outcomes of this effort deliver key datasets and methodologies, which enable new investigations within the research community, and contribute to the competitive advantage of America’s advanced manufacturing industries. These findings are the basis of virtual reality-based learning materials for undergraduate education, and middle- and high-school outreach. The objective of these instructional activities is to broaden participation in science, technology, engineering and mathematics (STEM) by leveraging virtual reality (VR) as a tool to convey materials scientific concepts to a broad range of students. Another intended outcome of these activities is the recruitment of students, including those from underrepresented groups, to participate in the research tasks of this effort, and thereby enhance the STEM pipeline.  Technical SummaryThe research focuses on the following question: How does the length scale of solute organization drive the deformation behavior of concentrated solid solutions? Within the context of concentrated systems, the motivation for this effort is the observed fluctuations in solute potential energies that emerge at the length scale of dislocations. These fluctuations underpin the central hypothesis of this investigation – that is, chemical short-range order gives rise to predictable, statistical heterogeneities in the potential energy landscape of concentrated solid solutions that influence the competition between various deformation mechanisms. To answer the question above, complementary experimental, including a nanobending testing technique, and computational research tools, such as scale-bridging kinetic Monte Carlo simulation, are being developed and utilized. The face-centered cubic CrCoNi system is selected as a benchmark for this investigation, yet the approach can be generalized to other concentrated systems of scientific and technological interest. Specific outcomes from this effort include 1) deformation mechanism maps that chart the trends in mechanism competition using chemical ordering as a structural parameter; 2) statistical relationships that link chemical short-range order with the length scale-resolved fluctuations in the potential energy barriers of deformation processes; and 3) a new experimental-computational approach to measure mesoscale deformation that bridges the temporal and spatial gap between simulations and theory. More broadly, the outcomes of this effort provide the research community with new tools to explore multiscale relationships in complex alloys, and key experimental datasets to validate interatomic potentials. The education and outreach activities feature virtual reality (VR) modules in order to illustrate concepts such as atomic packing, solid solution formation and slip.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.