CAREER: Understanding Microstructure Evolution and Deformation Mechanism of Strong yet Ductile Nanolamellar High-Entropy Alloys Produced by Additive Manufacturing

增材制造，也称为3D打印，是一种逐层生产网状部件的新范式，在汽车、航空航天、生物医学和其他行业有广泛的技术应用。除了巨大的设计自由度外，增材制造过程中的快速激光熔化可以在纳米尺度上生产高度精细的金属结构，以实现高强度。然而，高强度的纳米结构金属通常具有有限的延展性，即拉伸而不断裂的能力。这种强度和延展性的权衡一直是材料科学中一个长期存在的挑战，寻求同时提高强度和延性的材料一直是一个长期追求的目标。高熵合金（high -entropy alloys, HEAs）是一种新型材料，它含有高浓度的五种或五种以上不同的元素，且原子比例接近相等。与传统合金不同，传统合金主要由一种主要元素和少量合金元素组成。该学院早期职业发展（Career）奖支持对HEAs增材制造的基础研究，以实现超越当前基准的强度-延性协同作用。该项目通过集成微观结构表征、力学测试和计算建模，帮助了解控制3d打印HEAs机械性能的微观结构起源和变形机制。在这个项目中建立的知识将指导开发坚固而坚韧的金属合金，用于各种应用，如先进的能源系统，运输和国防。该职业奖还包括一个重要的教育组成部分，吸引学生在高中、本科和研究生阶段进行研究。通过扩大弱势群体的参与，该项目正在使材料科学和先进制造领域的下一代研究人员和STEM领导者多样化。技术概述3d打印金属合金通常涉及高度局部化的熔化过程，强温度梯度和快速冷却速度。这些极端的打印条件导致远离平衡状态，使微观结构细化到纳米级，以实现高强度。然而，高强度的纳米结构金属合金往往受到有限的延展性，被称为强度-延性权衡。利用激光增材制造的极端打印条件和HEAs良好的组成效应，在3d打印共晶HEAs中实现了双相纳米片嵌入微尺度共晶菌落的独特层次化微观结构。这个过程产生了强度和延展性的特殊组合。该职业奖旨在研究通过增材制造生产的这些强而韧性的纳米层状EHEAs的基本加工-结构-性能关系。本研究的科学目标是：1)了解激光打印方案如何影响3d打印共晶HEAs的凝固组织和力学性能。将开发工艺敏感热建模，以揭示复杂印刷参数与凝固微观结构和由此产生的机械性能之间的物理联系。2)利用原位中子衍射和透射电镜研究3d打印共晶HEAs的变形机理和微观力学响应。3)阐明3d打印共晶HEAs在打印后热处理后的相变途径。对非平衡3d打印HEAs退火过程中的相变途径和动力学进行了基本研究，以扩大材料设计的调色板。该CAREER项目提供的机理见解和设计主题对开发具有优异机械性能的分层、多相、纳米结构合金具有广泛的意义。该奖项还包括一项教育和推广计划，以推进下一代学生和弱势群体的研究培训和教育。将制定新的推广计划，如3D打印研讨会和夏季充实计划，以激励女性和未被充分代表的少数民族，并增加我们未来在材料科学和先进制造领域劳动力的多样性。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 SUMMARYAdditive manufacturing, also called 3D printing, is a new paradigm to produce net-shaped components layer by layer for a broad range of technological applications in automotive, aerospace, biomedical and other industries. In addition to vast design freedom, the rapid laser melting during additive manufacturing can produce highly refined structures at the nanoscale in metals for achieving high strength. However, high-strength nanostructured metals often suffer from limited ductility, which is an ability to be stretched without breaking. This strength-ductility tradeoff has been a long-standing challenge in materials science and the quest for materials that can simultaneously enhance strength and ductility has been a long-sought-after goal. High-entropy alloys (HEAs) are a new class of materials that contain high concentrations of five or more different elements in near equal atomic proportions, in contrast to traditional alloys that are primarily based on one major element with some minor alloying elements added. This Faculty Early Career Development (CAREER) award supports fundamental investigations into additive manufacturing of HEAs towards strength-ductility synergy beyond current benchmarks. This project is helping to understand the microstructural origin and deformation mechanism that govern the mechanical properties of 3D-printed HEAs by integrating microstructural characterization, mechanical testing, and computational modeling. The knowledge being established in this project will guide the development of strong yet tough metal alloys for various applications such as advanced energy systems, transportation, and defense. This CAREER award also includes a significant educational component that engages students in research across high school, undergraduate and graduate levels. Through broadening participation of underrepresented groups, this project is diversifying the next generation of researchers and STEM leaders in materials science and advanced manufacturing. TECHNICAL SUMMARY3D-printed metal alloys usually involve highly localized melting processes, strong temperature gradients, and fast cooling rates. These extreme printing conditions result in far-from-equilibrium states that enable microstructural refinement to the nanoscale for achieving high strength. However, high-strength nanostructured metal alloys often suffer from limited ductility, known as the strength-ductility tradeoff. Through harnessing the extreme printing conditions of laser additive manufacturing and favorable compositional effect of HEAs, a unique type of hierarchical microstructure in the form of dual-phase nanolamellae embedded in microscale eutectic colonies is achieved in 3D-printed eutectic HEAs. This process gives rise to an exceptional combination of strength and ductility. This CAREER award is investigating the fundamental processing-structure-property relationship in these strong yet ductile nanolamellar EHEAs produced by additive manufacturing. The scientific objectives in this study are to: 1) Understand how laser printing protocols affect the solidification microstructure and mechanical properties of 3D-printed eutectic HEAs. Process-sensitive thermal modeling will be developed to unveil the physical link between the complex printing parameters and the solidification microstructure and resulting mechanical properties. 2) Unravel the deformation mechanism and micromechanical response of 3D-printed eutectic HEAs by in situ neutron diffraction and transmission electron microscopy. 3) Elucidate the phase transformation pathways in 3D-printed eutectic HEAs upon post-printing heat treatment. A fundamental investigation of the phase transformation pathways and kinetics during annealing of the far-from-equilibrium 3D-printed HEAs are being performed to expand the palette for materials design. The mechanistic insights and design motifs being provided by this CAREER project have broad implications for the development of hierarchical, multi-phase, nanostructured alloys with excellent mechanical properties. This award also encompasses an educational and outreach plan to advance research training and education of next-generation students and underrepresented groups. New outreach initiatives such as 3D printing workshops and a summer-enrichment program will be developed to inspire women and underrepresented minorities and increase the diversity of our future workforce in materials science and advanced manufacturing.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.