Morphology dominated deformation mechanism of ultrahard nanostructured diamond

ZR Liu and TF Xu and Y Zhang and A Geng and D Legut and RF Zhang, CARBON, 242, 120426 (2025).

DOI: 10.1016/j.carbon.2025.120426

The strength of nano-polycrystalline diamond (nanodiamond) increases as the grain size decreases, owing to the suppression of the dislocation mobility within the grains and dislocation transmission across grain boundaries. However, at the nanoscale, grain boundary sliding begins to dominate, yielding an optimal size for peak strength. To harmonize both mechanisms, researchers have incorporated morphological effects to augment strength and toughness. In this paper, we present a comprehensive investigation employing atomic simulations of uniaxial compression on columnar and lamellar nanodiamonds with diverse grain aspect ratios, which underscore substantial mechanical anisotropy and remarkable enhancements in mechanical properties. Moreover, an increase of aspect ratios catalyzes a shift in failure mechanism from crack initiation to dislocation nucleation, transitioning nanodiamond deformation from brittle to ductile behavior. This transition is attributed to alterations in triple junction types, impeding nanocrack formation. Hence, we propose a straightforward design principle for nanodiamond morphology. Our findings not only offer insights into the distinct strengthening and toughening mechanisms in various nanodiamonds but also provide a rational blueprint for developing novel superhard carbon materials with exceptional performance.

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