CAREER: Asymmetrical Fracture of Two-Dimensional High Entropy Materials

该学院早期职业发展（Career）奖支持研究包含至少五种元素的二维原子厚高熵材料的断裂。二维材料，如石墨烯，通常倾向于脆性行为，这降低了用它们制造的电子、光子学和能量存储设备的机械稳定性。由于二维高熵材料在原子水平上具有更大的不对称性，因此有望具有更好的断裂韧性。因此，本项目支持合成单层和多层二维高熵材料的基础研究，在电子显微镜下进行断裂可视化实验，并从理论上再现实验观察到的行为。这项研究的见解将拓宽二维材料的家族，并促进对缺陷和其他因素对其力学性能和行为的影响的理解。由于具有更高的断裂韧性，二维高熵材料有可能取代或与现有材料集成，以生产高生命周期的纳米级器件。作为该项目的一部分，综合研究和教育计划将通过课堂/在线教育、知识传播、工程培训和外展活动努力产生社会影响。研究机会将提供给研究生和本科生，特别是代表性不足的少数民族学生。外展活动将针对K-12学生，以及独特的在家上学的学生，以激励他们接受STEM教育。受限于二维几何形状，裂纹通常导致脆性行为，在室温下塑性最小，这构成了块状材料断裂韧性和机械强度性能相互排斥的困境的基础。本研究旨在研究二维高熵材料的不对称断裂，裂纹尖端的不对称边缘弹性特性和裂纹扩展过程中的边缘交换导致了分岔、分支和挠度的出现，从而显著增加了断裂阻力。将通过固相反应和化学气相沉积方法合成各种二维高熵材料。在SEM和TEM中进行现场拉伸试验，以可视化各种微观组织缺陷和特征（如三元相和四相竞争）下的变形和断裂演变。基于DFT计算、数据驱动的MD模拟和相场建模的多尺度建模框架将用于模拟断裂行为，重点是裂纹的起裂和扩展。最终，该项目将促进对晶格畸变、缺陷、应变率、裂纹几何形状以及成分对二维高熵材料力学行为的影响的理解。该项目由民用、机械和制造创新部（CMMI）和刺激竞争研究的既定计划（EPSCoR）共同资助。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。

This Faculty Early Career Development (CAREER) award supports research to investigate fracture of two-dimensional atoms-thick high entropy materials containing at least five elements. Two-dimensional materials, such as graphene, generally favor a brittle behavior, which reduces mechanical stability of the electronics, photonics, and energy storage devices built with them. Two-dimensional high entropy materials are expected to possess substantially better fracture toughness owing to a greater asymmetry at the atomic level. Thus, this project supports fundamental research to synthesize monolayer and multiplayer two-dimensional high entropy materials, conduct experiments in electron microscopes to visualize fracture, and theoretically reproduce the experimentally observed behaviors. Insights from this study will broaden the family of two-dimensional materials and advance the understanding of the effect of defects and other factors on their mechanical properties and behaviors. With higher fracture toughness, two-dimensional high entropy materials could potentially replace or be integrated with existing materials to produce high lifecycle nanoscale devices. As part of the project, an integrated research and education program will strive for societal impacts through classroom/online education, knowledge dissemination, engineering training, and outreach activities. Research opportunities will be afforded to both graduate and undergraduate students, specially underrepresented minority students. Outreach activities will target K-12 students and, uniquely, homeschoolers to motivate them towards STEM education. Confined to two-dimensional geometry, cracks generally lead to brittle behavior with minimum plasticity at room temperature, which forms the basis of the dilemma of mutually exclusive fracture toughness and mechanical strength performance in bulk materials. This research aims to investigate asymmetrical fracture of two-dimensional high entropy materials, where bifurcations, branches, and deflections emerge due to asymmetric edge elastic properties at the crack tip and edge swapping during crack propagation, thus, significantly increasing the fracture resistance. Various two-dimensional high entropy materials will be synthesized via solid state reaction and chemical vapor deposition methods. In situ tensile tests in SEM and TEM will be conducted to visualize the deformation and fracture evolution amid various microstructural defects and features, such as the competing ternary and quaternary phases. A multiscale modeling framework based on DFT calculations, data-driven MD simulations, and phase field modeling will be used to simulate fracture behavior with focus on crack initiation and propagation. Ultimately, the project will advance the understanding of the effect of lattice distortion, defects, strain rate, and crack geometry as well as composition on the mechanical behavior of two-dimensional high entropy materials.This project is jointly funded by the Division of Civil, Mechanical and Manufacturing Innovation (CMMI) and the Established Program to Stimulate Competitive Research (EPSCoR).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.