Understanding the Hardening Mechanisms Associated with Short-Range Atom Clusters in High Entropy Alloys

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NONTECHNICAL SUMMARYThis award supports theoretical and computational research and education on mechanical behaviors of metallic materials. Metals and alloys are the workhorse materials for the manufacturing industry and structural applications. This is mainly because they have a good balance of strength, a metal's resistance to deformation and failure, and ductility, a metal's ability to undergo irreversible deformation before rupture. Usually there is a strength-ductility tradeoff, a gain in strength in a material is inevitably accompanied by a sacrifice in ductility. High entropy alloys are a new class of materials that contain nearly equal numbers of atoms of five or more different elements. Their unconventional concentrated multiple element compositions hold promise for achieving an exceptional combination of strength and ductility. However, the fundamental mechanisms that control the strength and ductility in high entropy alloys down to the atomic scale remain largely unexplored. This project focuses on investigation of the microscopic deformation mechanisms in high entropy alloys. Effects of the composition fluctuations on deformation processes mediated by defects in the periodic arrangement of atoms in the alloy will be studied by computer simulations on the scale of atoms; the results will be further compared with experiments. The physical insights gained will be important for guiding the future development of new high entropy alloys with a superior strength-ductility combination. The project will foster collaborations between theory and experiment. Educational activities will offer opportunities to introduce students to computer modeling techniques for simulating materials and to inspire students to pursue careers in science and engineering.TECHNICAL SUMMARYThis award supports theoretical and computational research and education to advance the fundamental understanding of deformation mechanisms in high entropy alloys. Strength and ductility are among the most important mechanical properties of metals and alloys for engineering applications. High entropy alloys contain high concentrations of five or more different elements in near equiatomic proportions. The mechanisms controlling the strength and ductility of high entropy alloys remain poorly understood. This project is focused on understanding the mechanistic role of short-range clusters in the strain hardening and tensile ductility of face-centered cubic high entropy alloys. Multi-component interatomic potentials will be used to perform molecular dynamics and atomistic reaction pathway simulations for studying the dislocation pinning and cross-slip processes mediated by short-range clusters. Effects of stress, temperature, cluster size and density will be investigated. The modeling results will be compared with experimental characterizations of dislocation mechanisms and deformation microstructures. The insights gained are important for harnessing the short-range clusters to achieve a superior strength-ductility combination in high entropy alloys. The project will introduce advanced modeling techniques to students. The research results will be incorporated into a high-school course module as well as a graduate course on micromechanics. Undergraduate students will be involved in the research. These educational activities are aimed to inspire students to pursue careers in science and engineering.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.