Tensile Properties and Fracture Behavior of Nanocrystalline Ni<sub>85</sub>W<sub>15</sub> Alloys Investigated via Molecular Dynamics Simulations

Nanocrystalline Ni85W15 alloys were computationally modeled as solid solutions with face-centered cubic (fcc) structures, incorporating random crystallographic orientations. Each alloy was enclosed within one of three hypothetical, space-filling polyhedral containers (crystallites): cubic (CB), truncated octahedron (TO), and rhombic dodecahedron (RD), in conjunction with a single-crystal (SC) configuration for comparison. The alloys were represented by 60 × 60 × 60 supercells containing 8.64 × 105 atoms to model the initial Ni85W15 configurations. These initial alloys were equilibrated at 300 K for 10 ps via molecular dynamics (MD) simulations utilizing a large-scale atomic/molecular massive parallel simulator (LAMMPS). Computational X-ray diffraction confirmed the formation of nanocrystalline structures in the CB, TO, and RD alloys. Subsequently, the equilibrated alloys were subjected to mechanical testing at 300 K for 30 ps (engineering strain, ε, in the range of 0–0.3 principally) with varying engineering strain rate (ε̇) of 10−2/ps (1010/s) for the 60 × 60 × 60 supercells, 10−2 and 10−3/ps (1010 and 109/s) for the 40 × 40 × 40 supercells, and 10−2, 10−3, and 10−4/ps (1010, 109, and 108/s) for the 20 × 20 × 20 supercells. At ε̇ and 10−3/ps, fractures were observed at the interfaces, where their normal vectors aligned with the tensile direction. Examples of fractures include alloys with a 40 × 40 × 40 supercell elongated along the z axis for the CB-type, diagonal of x, y, and z axes for the TO-type, and a 60 × 60 × 60 supercell along the diagonal of −x and y axes for the RD-type. The results demonstrated that morphological inhomogeneity owing to the presence of interfaces between crystallites can lead to fracture when subjected to a relatively high strain rates (ε̇ and 10−3/ps) in tensile MD simulations.