Recently, Prof. Wen Bin, Professor of the State Key Laboratory of Metastable Materials Preparation Technology and Science of Yanshan University, cooperated with scientists at home and abroad to make important progress in the research on the hardness mechanism of nano twinned diamonds. The research results are “Dislocation behaviors in nanotwinnedâ€. Diamond" (Nano-Crystal Diamond Dislocation Behavior) was published online September 21, 2018 on Science Advances.
Diamond is the hardest material in nature and is widely used in many fields such as scientific research and industry. In 2014, the research group of Professor Yan Yongjun of Yanshan University passed the compression of onion carbon to synthesize nano twinned diamond, which has twice the hardness of single crystal diamond, creating a new world record of material hardness, but the hardening mechanism is still unclear. How to understand the superhard mechanism of nanodiamonds has become a major topic in the research of superhard materials. Through the study of superhard mechanism, not only the understanding of the nature of hardness has important scientific significance, but also can provide new strategies for designing new materials with higher hardness. In response to this problem, the researchers first divided the slip of dislocation into three modes by analyzing the dislocation properties in nano twinned diamond: plug-in penetration mode, restricted slip mode and parallel twin boundary slip. mode. Then, by the molecular dynamics method, the critical shear stress of each of the three dislocation slip modes is calculated (Fig. 1). Finally, according to the Sachs model, the hardness of nano twinned diamonds with different twin thicknesses was obtained, and the calculated values ​​were in good agreement with the experimental results (Fig. 2). The results of this study show that the high hardness of nano twinned diamond depends mainly on two factors: one is the high lattice friction of diamond, and the other is the high non-thermally activated stress caused by the Holpech effect.
Fig.1 Calculated value of critical slitting stress of nano twinned diamond
Fig. 2 Comparison of calculated and experimental values ​​of nano twinned diamond hardness
Yanshan University is the first unit of the thesis. Xiao Jianwei, a doctoral student at Yanshan University, is the first author and the author of the communication is Professor Wen Bin. The research work was funded by the National Natural Science Foundation of China (project number, 51372215, 51332005).
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