"Nature" published the results of Yanshan University's superhard materials technology
First synthesis of cubic boron nitride of hardness super diamond single crystal
On January 18, the reporter learned from Yanshan University that the research team led by Professor Tian Yongjun of the State Key Laboratory of Metastable Materials Preparation Technology and Science of Yanshan University and Professor Ma Yuming of the State Key Laboratory of Superhard Materials of Jilin University, Professor Wang Yanbin of the University of Chicago and Hebei Industry Professor Tang Chengchun and other scientists have made breakthroughs in the research of polycrystalline superhard material synthesis technology and hardening mechanism of superhard materials. The ultra-high hardness nano-crystalline cubic boron nitride bulk material was successfully synthesized by high temperature and high pressure technology. The research results were published in the latest issue of Nature magazine on January 17, 2013. The results of this research mark the first time that humans have obtained synthetically harder materials than diamond single crystals. This has also broken through the traditional understanding of the hardening mechanism of materials and found a new way to synthesize high-performance superhard materials.
According to reports, cubic boron nitride is an important superhard material and has been widely used in the iron-based material processing industry. Unfortunately, the synthetic cubic boron nitride single crystal is less than half the hardness of a diamond single crystal. According to the well-known Hall-Petch relationship, the hardness of polycrystalline materials increases with decreasing grain size. Therefore, the synthesis of nanostructured cubic boron nitride has become an effective means to improve hardness. Using the martensitic transformation of graphite-like boron nitride precursors at high temperatures and pressures, scientists have synthesized nanocrystalline cubic boron nitrides with a minimum grain size of 14 nanometers. Tian Yongjun and his collaborators successfully synthesized a transparent nano-twisted cubic boron nitride using a special structure of onion boron nitride as a precursor. The average thickness of twins is only 3.8 nm, and its hardness reaches or exceeds artificial. The synthesized diamond single crystal has higher fracture toughness than commercial cemented carbide, and the oxidation resistance temperature is higher than that of the cubic boron nitride single crystal itself. These excellent comprehensive properties indicate that the nano twin structure cubic boron nitride is a long-awaited tool material in the industry. This research demonstrates a new way to synthesize high-performance superhard materials – obtaining ultra-fine nano twin structures.
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