Abstract
Over the past several decades, great endeavors have been devoted to superhard materials research, among which two topics are of central focus. One is to understand hardness microscopically and reveal the controlling factors for superhardness, which can be used to guide the design of novel superhard crystals; the other is to synthesize superhard materials with enhanced comprehensive performance (i.e., hardness, fracture toughness, and thermal stability), with the ambition to synthesize materials harder than natural diamond. We proposed a microscopic understanding of the indentation hardness as the combined resistance of chemical bonds in a material to indentation, and established a microscopic hardness model for covalent and polar covalent crystals, which was further generalized to polycrystalline materials. Guided by the polycrystalline hardness model, we successfully synthesized nanotwinned cubic boron nitride and diamond bulks under high pressure and high temperature. These materials exhibit simultaneous improvement of hardness, fracture toughness, and thermal stability, designating a new direction for superhard materials research.
摘要
半个世纪以来, 超硬材料研究领域一直存在两个重要难题亟待解决: (1) 硬度的微观理论或超硬材料的设计原理; (2) 合成出综合性能(硬度、 韧性和热稳定性)更加优异的新型超硬材料, 尤其是实现人工材料比天然金刚石更硬这一梦想. 在过去的十多年里, 我们提出了一个基本假设—微观上硬度等于晶体单位面积中化学键对压入的综合阻抗, 由此建立了共价和极性共价晶体硬度的微观模型, 实现了晶体硬度的定量预测. 随后, 我们将晶体硬度的微观模型推广至多晶固体, 建立了多晶共价材料硬度的理论模型. 最近, 以多晶硬度模型为指导, 我们在高温高压条件下分别合成出纳米孪晶结构的立方氮化硼和金刚石块材. 与单晶材料相比, 纳米孪晶立方氮化硼和金刚石的硬度、 韧性和热稳定性均得到明显改善, 为发展高性能超硬材料探索出一条崭新的途径.
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Bo Xu is a professor of College of Materials Science and Engineering, Yanshan University. He received his PhD from University of Nebraska-Lincoln (2002). After postdoctoral work at University of Maryland, College Park, he joined the State Key Laboratory of Metastable Materials Science and Technology, Yanshan University in 2006. His research interests include superhard materials and thermoelectric materials.
Yongjun Tian is a professor of College of Materials Science and Engineering, Yanshan University. He received his PhD from Institute of Physics, Chinese Academy of Sciences, in 1994, and worked as a postdoctoral fellow in Universität Jena supported by the Humboldt Research Fellowships from 1996 to 1998. His research interests include design and synthesis of novel metastable materials.
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Xu, B., Tian, Y. Superhard materials: recent research progress and prospects. Sci. China Mater. 58, 132–142 (2015). https://doi.org/10.1007/s40843-015-0026-5
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DOI: https://doi.org/10.1007/s40843-015-0026-5