CAREER: Defect Energetics and Dynamics in Concentrated Alloys

金属合金作为结构材料广泛应用于许多实际应用中，如桥梁、发电厂、建筑物、飞机和汽车。传统合金通常由一种主要合金元素和其他低浓度合金元素组成，以改善合金性能。近年来，浓缩合金因其新颖的性能而受到广泛关注。与传统合金不同，浓缩合金由两种或两种以上的主要合金元素组成。与传统合金相比，这些浓缩合金具有优异的物理性能，包括高温强度、耐腐蚀性、耐辐射以及耐磨损和抗疲劳性。这种优异的性能与浓缩合金中晶体缺陷的独特形成和传输机制有关，迄今为止人们对这一机制知之甚少。该项目的目标是使用新颖的计算方法来缩小这一知识差距。本研究将研究合金成分、合金元素的原子构型、合金元素之间的相互作用对高浓度合金中缺陷形成和输运机制的影响。评估原子机制与长期缺陷演变之间的联系，以了解这些机制对合金微观组织演变的重要性。该项目的成功完成将揭示导致浓缩合金中独特缺陷特性的原子起源。这一认识有助于建立基于科学的原则来选择合金元素，以控制浓缩合金中的缺陷扩散和质量传递，从而获得所需的物理性能。在弗吉尼亚理工大学的两个拓展项目中，通过实验室课程和实际操作的计算机模拟培训，该项目旨在从代表性不足的群体中招募高中学生进入工程学科，该项目将有助于吸引和招募具有不同背景的下一代材料科学家和工程师。此外，该研究将纳入本科和研究生课程，以教育和留住学生在计算材料科学和物理冶金。晶格缺陷如间隙和空位及其团簇是材料中主要的质量输运载体。它们的扩散是控制材料微观结构演变和物理性能变化的关键过程。虽然缺陷能量学和动力学在纯金属和稀合金中得到了很好的研究，但在包括高熵合金在内的浓合金中却知之甚少。本项目的主要目的是了解浓缩合金中独特缺陷的原子起源，如缓慢扩散，这是由合金元素的复杂原子构型和相互作用进一步决定的。今后的研究将从二元浓缩合金开始，逐步扩展到三元合金和高熵合金。将使用多尺度建模方法，包括分子静力学、分子动力学、温度加速动力学和簇动力学。为了了解原子构型的影响，将研究不同成分的合金，包括渗透阈值，以阐明渗透是否导致合金元素的优先扩散。对于原子间相互作用的影响，将以期望的方式选择合金元素之间的不同相互作用，以确定缺陷形成能和迁移势垒对缓慢扩散的相对重要性。温度加速动力学将用于研究非直观的缺陷簇迁移机制，该机制可以达到长时间尺度，但具有完全的原子保真度。在实验可及的时间尺度上，簇动力学将用于评估不同类型缺陷和簇对长期缺陷演化的重要性。完成这些任务将有助于了解浓缩合金中独特的缺陷形成和传输机制，并可能有助于研究团体设计具有最佳性能的新型合金。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。

NON-TECHNICAL SUMMARYMetallic alloys are widely used as structural materials in many practical applications such as bridges, power plants, buildings, aircrafts, and automobiles. Conventional alloys are typically made of one principal alloying element with addition of other low-concentration alloying elements for improving alloy properties. Recently, concentrated alloys have received significant interests due to their novel properties. Different from conventional alloys, concentrated alloys consist of two or more principal alloying elements. These concentrated alloys exhibit outstanding physical properties compared to conventional alloys including high-temperature strength, corrosion resistance, radiation tolerance, as well as wear and fatigue resistance. Such superior properties are related to the unique formation and transport mechanisms of crystal defects in concentrated alloys, which are poorly understood to date. The goal of this project is to use novel computational approaches to narrow this knowledge gap. The proposed research will study the effects of alloy composition, atomic configuration of alloying elements, interaction between alloying elements on the defect formation and transport mechanisms in concentrated alloys. The connection between the atomistic mechanisms and long-term defect evolution will be assessed to understand the importance of these mechanisms on the microstructural evolution in alloys. Successful completion of this project will reveal the atomic origins that lead to the unique defect properties in concentrated alloys. The understanding may help establish science-based principles for down-selecting alloying elements to control defect diffusion and mass transport in concentrated alloys and thus achieve desired physical properties. Through laboratory sessions and hands-on computer simulation training at two outreaching programs at Virginia Tech that target on recruiting high school students from under-represented groups into engineering disciplines, this project will help attract and recruit next-generation materials scientists and engineers with diverse backgrounds. In addition, the research will be integrated into both undergraduate and graduate courses to educate and retain students in computational materials science and physical metallurgy. TECHNICAL SUMMARYLattice defects such as interstitials and vacancies as well as their clusters are main mass transport carriers in materials. Their diffusion is a critical process for governing the microstructural evolution and thus the change of physical properties in materials. Although defect energetics and dynamics are well studied in pure metals and dilute alloys, they are poorly understood in concentrated alloys including high-entropy alloys. The main objective of this project is to understand the atomic origins for the unique defect energetics and dynamics in concentrated alloys such as sluggish diffusion, which are further determined by the complex atomic configurations and interactions of alloying elements. The proposed research will start from binary concentrated alloys and gradually extend to ternary alloys and high-entropy alloys. Multiscale modeling methods including molecular statics, molecular dynamics, temperature accelerated dynamics, and cluster dynamics will be used. To understand the effect of atomic configuration, alloys of different compositions including the percolation threshold, will be studied to elucidate whether percolation leads to preferential diffusion of alloying elements. For the effect of interatomic interaction, different interactions between alloying elements will be selected in a desired way to determine the relative importance between defect formation energies and migration barriers on the sluggish diffusion. Temperature accelerated dynamics will be used to study the non-intuitive defect cluster migration mechanisms, which can reach long timescales but with full atomic fidelity. Cluster dynamics will be used to evaluate the importance of different types of defects and clusters on the long-term defect evolution at the experimentally accessible timescales. Accomplishing these tasks will enable understanding of the unique defect formation and transport mechanisms in concentrated alloys and may help the research community design novel alloys of optimum properties.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.