Tuning Nanostructured Morphology in Superhard Metal Borides

点击翻译按钮获取中文摘要

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.