Dynamic recrystallization of Silver nanocubes during high-velocity impacts

Abstract

We study microstructural evolution of Silver (Ag) single-crystal nanocubes during high-velocity impacts, their dynamic recrystallization, and post-impact lattice structure using a combination of molecular dynamics and ab-initio simulations. Our study shows that, upon the impact, some preferential orientations can develop intricate, architected microstructures with grains of different sizes. These selected orientations correspond to the cases where at least eight or more slip systems are simultaneously activated, leading to an avalanche of dislocations. These dislocations interact and have the ability to produce severe plastic work, stimulating recrystallization in the nanocubes. On the other hand, dynamic recrystallization is not observed for the orientations with asynchronously activated slip systems besides large shock-wave pressures, plastic deformation, and large dislocation densities. Using thermalized ab-initio simulations, we find that the severe plastic deformation can trigger phase transformation of the initial face-centered cubic lattice structure to the 4H hexagonal closed-packed phase, which is thermodynamically more stable than the 2H hexagonal closed-packed phase. These results are in good agreement with experimental works. Our systematic numerical experiments shed light on the factors that promote dynamic recrystallization and provide a pathway to control the microstructure and atomic structure simultaneously by orienting nanocubes during the impact.