Structure and energetics of nanotwins in cubic boron nitrides

Journal Article · Mon Aug 22 00:00:00 EDT 2016 · Applied Physics Letters

DOI:https://doi.org/10.1063/1.4961240· OSTI ID:22590518

Zheng, Shijian; Ma, Xiuliang ^[1]; Zhang, Ruifeng ^[2]; Huang, Rong ^[3]; Taniguchi, Takashi ^[4]; Ikuhara, Yuichi ^[5]; Beyerlein, Irene J. ^[6]

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1. Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China)
2. School of Materials Science and Engineering, and International Research Institute for Multidisciplinary Science, Beihang University, Beijing 100191 (China)
3. Key Laboratory of Polar Materials and Devices, Ministry of Education, East China Normal University, Shanghai 200062 (China)
4. National Institute for Materials Science, Tsukuba, Ibaraki 305-0044 (Japan)
5. Nanostructures Research Laboratory, Japan Fine Ceramics Center, Nagoya 456-8587 (Japan)
6. Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

Recently, nanotwinned cubic boron nitrides (NT c-BN) have demonstrated extraordinary leaps in hardness. However, an understanding of the underlying mechanisms that enable nanotwins to give orders of magnitude increases in material hardness is still lacking. Here, using transmission electron microscopy, we report that the defect density of twin boundaries depends on nanotwin thickness, becoming defect-free, and hence more stable, as it decreases below 5 nm. Using ab initio density functional theory calculations, we reveal that the Shockley partials, which may dominate plastic deformation in c-BNs, show a high energetic barrier. We also report that the c-BN twin boundary has an asymmetrically charged electronic structure that would resist migration of the twin boundary under stress. These results provide important insight into possible nanotwin hardening mechanisms in c-BN, as well as how to design these nanostructured materials to reach their full potential in hardness and strength.

• OSTI ID: 22590518
• Journal Information: Applied Physics Letters, Vol. 109, Issue 8; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA); ISSN 0003-6951
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
BORON NITRIDES
DENSITY
DENSITY FUNCTIONAL METHOD
ELECTRONIC STRUCTURE
HARDNESS
NANOSTRUCTURES
PLASTICITY
THICKNESS
TRANSMISSION ELECTRON MICROSCOPY