Atomic Simulation of Crystallographic Orientation Effect on Void Shrinkage and Collapse in Single-Crystal Copper under Shock Compression

Abstract

Molecular dynamics simulations were performed to study the evolution of void along different crystallographic orientations of single-crystal copper under shock compression, including $[1\overline{{{\kern 1pt} 1{\kern 1pt} }} 0]$, $[111]$ and $[100]$ orientations. For both $[1\overline{{{\kern 1pt} 1{\kern 1pt} }} 0]$ and $[111]$ directions, the void only shrinks and does not collapse, whereas for $[100]$ direction, the void can gradually shrink until it collapses completely. Dislocations react with each other to form sessile dislocations during the continuous loading of the shock waves, in both $[1\overline{{{\kern 1pt} 1{\kern 1pt} }} 0]$ and [111] directions, and almost all the dislocations are found to be $\frac{a}{6} < 110 >$ stair-rod partial dislocations which are of sessile type. However, for the [100] orientation, sessile dislocations are mainly $\frac{a}{3} < 001 >$ Hirth partial dislocations. For $[100]$ direction, the sessile dislocation density is the lowest among the three orientations. Therefore, shock compression along $[100]$ direction is more conducive to plastic deformation of the void. Dislocation slip is responsible for deformation mechanism of the void, where $\frac{a}{6} < 112 >$ Shockley partial dislocations are firstly generated on the surface of the void, and then they continue to move and multiply, which shall lay the foundation for the formation of stacking faults. Stacking faults sweep through the crystal plane and consequently the void shrinks. This work gives an atomic-scale observation perspective of the evolution of micro-void defects in single-crystal copper under shock compression and provides a clearer explanation for the understanding of the dislocation evolution mechanism behind the deformation.