Tuning Nanostructured Morphology in Superhard Metal Borides

非技术概述：机械硬度是决定材料在机械加工和制造行业中应用的重要性能。由于硬质材料作为刀具和磨料的广泛使用，对超硬材料的需求一直在稳步增长。最著名的超硬材料--钻石--在切割和钻探钢铁方面并不有效，因为它在空气中的热稳定性很差，而且容易与它试图切割的钢中的铁反应。因此，寻找传统超硬材料的替代品引起了人们的极大兴趣。它们在建筑、汽车和其他行业中是需要的，以取代昂贵和低性能的传统硬质材料，如碳化钨。为了解决这些问题，首席调查员(PI)正在设计新一代超硬材料，这种材料将大大提高硬度，并能够以较低的成本切割钢和其他材料。受天然钻石独特性质的启发，首席研究人员专注于在其他化合物中创建具有类似性质的网络，重点是富电子金属和硼的混合物。这种新型超硬材料是在常压下合成的，并将进行表征，以了解材料结构与硬度之间的关系。PIs的教育努力满足了从小学到大学本科生的各种需求，包括课程开发、为大洛杉矶地区的小学、初中和高中举办的教师讲习班，以及学校外展访问。劳动力发展是通过培训研究生来实现的，研究生还通过研究协助外展项目和指导加州大学洛杉矶分校的本科生。该项目由材料研究部的固态和材料化学计划支持。技术摘要：硬度是一种物理现象，取决于材料的化学键强度和颗粒结构。因此，对如何设计新的超硬材料的理解需要充分的机械洞察力和对结合和颗粒形态的控制。为了应对这一挑战，首席研究人员(PI)正在将各种过渡金属硼化物系统的合成与高压研究结合起来，以获得关于各种块状和纳米材料中塑性变形的晶格特定信息。这些金属硼化物结构由高价电子密度金属与多个短硼-硼键结合而成，提供了一个高共价键网络，可防止滑移和位错，并结合高静电斥力来抵抗键压缩。这项拟议工作的目标是在材料研究部固态和材料化学计划的支持下，综合控制晶粒度和形貌。在块状材料中，这是通过分解WB4系统中的亚稳十二硼化物相和析出ReB2系统中的第二相来实现的。此外，熔盐法正在被用来开发纳米颗粒尺寸的金属硼化物，如纳米ReB2和纳米WB4。因此，这些合成方法旨在提高块体和纳米材料的外部硬度。材料正在通过维氏硬度测试和钻石顶压室的高压实验进行分析。在了解了键合和颗粒形态的耦合效应后，该研究小组的目标是系统地调整纳米结构材料，并推动下一代超硬金属硼化物的发展。这项工作的更广泛的影响在于通过培训研究生来发展劳动力，从小学到大学本科生的PI的广泛的外展努力，以及对商业切割、钻探和机械加工行业的重大潜在影响。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。

NON-TECHNICAL SUMMARY:Mechanical hardness is an important property used to determine the applications of materials in the machining and manufacturing industries. Due to the extensive use of hard materials as cutting tools and abrasives, the demand for superhard materials has been steadily increasing. The best-known superhard material – diamond – is not effective at cutting and drilling steel due to its poor thermal stability in air and its tendency to react with the iron in the steel it is trying to cut. Therefore, there is great interest in finding alternatives to traditional superhard materials. These are needed in the construction, automotive, and other industries to replace costly and low performing traditional hard materials like tungsten carbide. To address these issues, the Principal Investigators (PIs) are designing a new generation of superhard materials that will provide greatly increased hardness and the ability to cut steels and other materials at lower cost. Inspired by the unique properties of natural diamond, the Principal Investigators have focused on creating networks with similar properties in other compounds, focusing on mixtures of electron-rich metals and boron. The novel superhard materials are synthesized at ambient pressure and characterization will be conducted to understand the correlation between material structure and hardness. The educational efforts of the PIs, which address the needs of students ranging from elementary school to college undergraduates, include course development, teacher workshops for elementary, middle, and high schools in the greater Los Angeles area, and school outreach visits. Workforce development occurs through the training of graduate students, who also assist with outreach programs and mentor UCLA undergraduate students through research. This project is supported by the Solid State and Materials Chemistry program within the Division of Materials Research.TECHNICAL SUMMARY:Hardness is a physical phenomenon dependent on both the chemical bond strength and grain structure of a material. An understanding of how to design new superhard materials thus requires sufficient mechanistic insight and control of both bonding and grain morphology. To address this challenge, the Principal Investigators (PIs) are combining the synthesis of a wide range of transition metal boride systems with high-pressure studies to obtain lattice-specific information about plastic deformations in a broad range of bulk and nanoscale materials. These metal boride structures consist of high valence electron density metals, combined with multiple short boron-boron bonds, providing a highly covalent bonding network that is resistant to slip and dislocations, combined with high electrostatic repulsion that resists bond compression. The goal of the proposed work, supported by the Solid State and Materials Chemistry program within the Division of Materials Research, is to synthetically control both grain size and morphology. In bulk materials, this is being accomplished through the decomposition of metastable dodecaboride phases in the WB4 system and through precipitation of secondary phases in the ReB2 system. Additionally, molten salt methods are being used to develop nano grain-sized metal borides such as nano-ReB2 and nano-WB4. These synthetic approaches thus aim to enhance extrinsic hardness in both bulk and nano-sized materials. Materials are being analyzed through Vickers hardness testing and high-pressure experiments in diamond anvil cells. With an understanding of the coupled effects of bonding and grain morphology, the research team aims to systematically tune nanostructured materials and advance the next generation of superhard metal borides. The broader impacts of the work lie in workforce development through the training of graduate students, in the extensive outreach efforts of the PIs, which address the needs of students ranging from elementary school to college undergraduates, and in the significant potential for impact on the commercial cutting, drilling and machining industries.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.