Collaborative Research: Interface enabled plasticity in high-strength Co-based intermetallics

高强度和高变形性材料的设计对于下一代结构应用至关重要，可以改变国防系统和工业，如航空航天，汽车和能源。金属间化合物具有高机械强度和高熔融温度的显著特性，是这些应用的优秀候选者。然而，传统的金属间化合物在室温下非常脆，这对它们作为结构材料的潜力产生了不利影响。尽管近几十年来金属间化合物一直是研究的热点，但在室温下保持高强度的同时实现塑性一直是一个重大挑战。先前提高金属间化合物塑性的方法主要集中在通过细化晶粒、提高晶界内聚强度和引入第二相颗粒来提高抗断裂能力。初步研究表明，具有非常规厚晶界的煤纳米复合材料具有超高强度和高变形性。然而，支撑这些显著特性的基本机制仍不清楚。通过纳米加工、原位纳米力学测试和原子模型的协同结合，他们在原子水平上阐明了核/壳纳米复合材料的变形机制。研究人员之间的密切合作使研究生和本科生通过每两周一次的视频会议和每年对对口机构的访问，在实验和模拟方面打下良好的基础。研究生还可以使用由洛斯阿拉莫斯国家实验室和桑迪亚国家实验室管理的集成纳米技术中心内的先进显微镜设备。调查人员为拟议的项目招募少数民族学生。这个项目制作的标本在美国宇航局的国际空间站进行测试。本项目的目标是了解具有新颖核/壳结构的纳米晶（NC）金属间化合物的力学行为，这种结构赋予它们在室温下同时具有高强度和前所未有的可变形性。研究人员通过原位纳米压痕和原子模拟来探索核/壳复合材料的变形机制，以阐明纳米晶金属间化合物的晶界主导塑性，量化厚界面对核/壳纳米复合材料中煤金属间化合物的强化和变形能力的影响。通过SEM原位微压缩实验和分子动力学模拟，了解核/壳纳米复合材料的高温变形机理。该研究项目极大地促进了对变形机制的理解，以及具有非常规核/壳结构的金属间化合物的设计和制造，用于关键结构应用。这项工作为“厚”晶界提供了原子的见解，作为非凡机械性能的新图案，为通过晶界工程合理设计其他金属间化合物开辟了道路。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 SummaryThe design of high strength and high deformability materials is critical for next-generation structural applications that can transform the national defense systems and industries such as aerospace, automotive, and energy. Intermetallics, with their remarkable properties of high mechanical strength and high melting temperatures, are excellent candidates for these applications. However, conventional intermetallics are very brittle at room temperature, which adversely impacts their potential as structural materials. Although intermetallics have been the subject of active research in recent decades, achieving room temperature plasticity while retaining high strength has been a major challenge. Prior approaches to improve plasticity in intermetallics have primarily focused on improving fracture resistance by grain refinement, improving grain boundary cohesive strength and introducing second phase particles. The investigators’ preliminary studies reveal that CoAl nanocomposites with unconventional thick grain boundaries exhibit ultra-high strength and high deformability. However, the fundamental mechanisms underpinning these remarkable properties remain unclear. Through the synergistic combination of nanofabrication, in situ nanomechanical testing and atomistic modeling, they elucidate the deformation mechanisms in core/shell nanocomposites at an atomistic level. The close collaboration among the investigators enable graduate and undergraduate research students to develop a wholesome foundation in both experiments and simulations through biweekly videoconferences, and annual visits to counterpart institutions. Graduate students also access advanced microscopy facilities housed within the Center for Integrated Nanotechnologies managed by Los Alamos National Lab and Sandia National Lab. The investigators recruit minority students for the proposed project. The specimens fabricated from this project are tested at NASA’s International Space Station. Technical SummaryThe goal of this project is to understand the mechanical behavior of nanocrystalline (NC) intermetallics with a novel core/shell architecture that endows them with simultaneous high strength and unprecedented deformability at room temperature. The investigators explore the deformation mechanisms in core/shell composites via integrated in situ nanoindentation and atomistic simulations to elucidate grain boundary dominated plasticity in nanocrystalline intermetallics, quantify the impact of thick interfaces on strengthening and deformability of CoAl intermetallics in core/shell nanocomposites, and understand the high temperature deformation mechanisms of core/shell nanocomposites by combining in situ microcompression tests in SEM and molecular dynamics simulations. The research program significantly advances the understanding of the deformation mechanisms, design and fabrication of intermetallics with unconventional core/shell architecture for critical structural applications. This work furnishes atomistic insights into “thick” grain boundary as novel motifs for extraordinary mechanical properties that open up avenues for the rational design of other intermetallics through grain boundary 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.