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

非技术概述高强度和高变形材料的设计对于能够改变国防系统和航空航天、汽车和能源等行业的下一代结构应用至关重要。金属间化合物具有高机械强度和高熔化温度的显著特性，是这些应用的极佳候选材料。然而，传统的金属间化合物在室温下非常脆，这对其作为结构材料的潜力造成了不利的影响。虽然金属间化合物在近几十年来一直是活跃研究的主题，但在保持高强度的同时实现室温塑性一直是一个重大挑战。以往改善金属间化合物塑性的方法主要集中在通过细化晶粒、提高晶界结合强度和引入第二相粒子来提高断裂抗力。研究人员的初步研究表明，具有非常规粗晶界的煤纳米复合材料具有超高的强度和高的变形能力。然而，支撑这些非凡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拟的协同结合，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能够通过两周一次的视频会议和每年对对应机构的访问，在实验和模拟方面建立一个健康的基础。研究生还可以参观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施。调查人员为拟议的项目招收少数族裔学生。该项目制作的样品在NASA的国际空间站进行了测试。本项目的目标是了解具有新型核/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变形能力。研究人员通过集成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，以阐明纳米金属间化合物中晶界主导的塑性，量化厚界面对核/壳纳米复合材料中煤金属间化合物强化和变形能力的影响，并结合扫描电子显微镜的原位微压缩实验和分子动力学模拟来了解核/壳纳米复合材料的高温变形机制。该研究项目极大地促进了对金属间化合物的变形机制、设计和制造的理解，这些金属间化合物具有用于关键结构应用的非传统核/壳结构。这项工作为“厚”晶界提供了原子学的洞察力，作为非凡的机械性能的新主题，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NSF的法定使命，并通过使用基金会的智力优势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.