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

该奖项支持金属材料力学行为的理论和计算研究以及教育。金属和合金是制造业和结构应用的主要材料。这主要是因为它们具有良好的强度平衡，金属的抗变形和破坏能力，以及延展性，金属在破裂前经历不可逆变形的能力。通常存在强度和延性的权衡，材料强度的增加不可避免地伴随着延性的牺牲。高熵合金是一类包含五种或五种以上不同元素的原子数量几乎相等的新材料。其非常规的集中多元素组成有望实现强度和延展性的特殊组合。然而，将高熵合金的强度和延展性控制到原子尺度的基本机制在很大程度上仍未被探索。本项目主要研究高熵合金的微观变形机制。在原子尺度上进行计算机模拟，研究合金中成分波动对原子周期性排列缺陷介导的变形过程的影响；本文将进一步与实验结果进行比较。所获得的物理见解将对指导具有优越强度-塑性组合的新型高熵合金的未来发展具有重要意义。这个项目将促进理论与实验之间的合作。教育活动将提供机会，向学生介绍模拟材料的计算机建模技术，并激励学生从事科学和工程方面的职业。该奖项支持理论和计算研究和教育，以促进对高熵合金变形机制的基本理解。强度和延展性是工程应用中金属和合金最重要的机械性能。高熵合金含有高浓度的五种或五种以上不同的元素，其原子比例接近等。控制高熵合金强度和延展性的机制仍然知之甚少。本项目的重点是了解近程团簇在面心立方高熵合金应变硬化和拉伸延性中的机制作用。多组分原子间电位将用于进行分子动力学和原子反应途径模拟，以研究由短程团簇介导的位错钉住和交叉滑移过程。研究了应力、温度、簇大小和密度的影响。模拟结果将与位错机制和变形微观组织的实验表征进行比较。所获得的见解对于利用短程团簇在高熵合金中实现卓越的强度-延展性组合具有重要意义。该项目将向学生介绍先进的建模技术。研究成果将被纳入高中课程模块和研究生微力学课程。本科生将参与研究。这些教育活动旨在激励学生从事科学和工程方面的职业。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.