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:1420658

Zheng, Shijian; Zhang, Ruifeng; Huang, Rong; Taniguchi, Takashi; Ma, Xiuliang; Ikuhara, Yuichi; Beyerlein, Irene J.

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.

• Sponsoring Organization: USDOE
• OSTI ID: 1420658
• Journal Information: Applied Physics Letters, Journal Name: Applied Physics Letters Vol. 109 Journal Issue: 8; ISSN 0003-6951
• Publisher: American Institute of Physics
• Country of Publication: United States
• Language: English