Extreme mechanical anisotropy in diamond with preferentially oriented nanotwin bundles
YL Pan and P Ying and YF Gao and P Liu and K Tong and DL Yu and KL Jiang and WT Hu and BZ Li and B Liu and ZS Zhao and JL He and B Xu and ZY Liu and YJ Tian, PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 118, e2108340118 (2021).
Mechanical properties of covalent materials can be greatly enhanced with strategy of nanostructuring. For example, the nanotwinned diamond with an isotropic microstructure of interweaved nanotwins and interlocked nanograins shows unprecedented isotropic mechanical properties. How the anisotropic microstructure would impact on the mechanical properties of diamond has not been fully investigated. Here, we report the synthesis of diamond from superaligned multiwalled carbon nanotube films under high pressure and high temperature. Structural characterization reveals preferentially oriented diamond nanotwin bundles with an average twin thickness of ca. 2.9 nm, inherited from the directional nanotubes. This diamond exhibits extreme mechanical anisotropy correlated with its microstructure (e.g., the average Knoop hardness values measured with the major axis of the indenter perpendicular and parallel to nanotwin bundles are 233 +/- 8 and 129 +/- 9 GPa, respectively). Molecular dynamics simulation reveals that, in the direction perpendicular to the nanotwin bundles, the dense twin boundaries significantly hinder the motion of dislocations under indentation, while such a resistance is much weaker in the direction along the nanotwin bundles. Current work verifies the hardening effect in diamond via nanostructuring. In addition, the mechanical properties can be further tuned (anisotropy) with microstructure design and modification.
Return to Publications page