研究目的
To investigate the dependence of mechanical properties on the grain size (d) of nanocrystalline diamond (NCD) using molecular dynamics (MD) simulations.
研究成果
The mechanical properties of NCD are sensitive to grain size (d). The Young's modulus (E) increases with the increase of d due to the increasing fraction of grain interiors (GIs), while the failure strain (εf) and failure strength (σf) decrease with the increase of d. The deformation work density increases with the decrease of d, indicating the enhancement of toughness of NCD when d is small. The nucleation and propagation of both transgranular and intergranular cracks are the main failure mechanisms.
研究不足
The study is limited to the grain size range of 2 nm to 9 nm and does not explore the effects of impurities and defects that may exist in realistic samples. The time scale in MD simulations is picosecond, which is much larger than that in experiment.
1：Experimental Design and Method Selection:
Molecular dynamics (MD) simulations were performed to investigate the mechanical behavior of 3D NCD with various grain sizes (d). The Tersoff potential was used to describe the interactions between atoms in materials with strong covalent bonds.
2：Sample Selection and Data Sources:
A set of 3D NCD atomic structures with d = 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, and 9 nm were constructed by the Voronoi construction with 27 random 'seeds'.
3：List of Experimental Equipment and Materials:
MD simulations were performed with LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator).
4：Experimental Procedures and Operational Workflow:
Each sample was relaxed at 300 K using a Nose-Hoover thermostat and a Nose/Hoover pressure barostat for 600 ps to reach an equilibrium state. Uniaxial elongation was applied to each sample at the strain rate of 1 × 10^9 s^-1 and the temperature of 300 K.
5：Data Analysis Methods:
The program OVITO was adopted to visualize and analyze the simulation results, and the Identify Diamond Structure (IDS) method was used to detect defects and their evolution.
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