Dynamic Recrystallization of Silver Nanoparticles During High-Velocity Impacts

We study high-velocity impacts of Silver (Ag) single crystals nanocubes, 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 have the potential to develop an intricate, architected microstructures with grains of different sizes. These selected orientations correspond to the cases where at least eight or more slip systems were simultaneously activated, leading to an avalanche dislocations. These dislocations interact and have the ability to produce severe plastic work, stimulating recrystallization in the particles. On the other hand, dynamic recrystallization was not observed for the orientations with asynchronously activated slip systems besides  large shock-wave pressures, plastic deformations, and large dislocation densities. In addition, using thermalized ab-initio simulations, we found 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 into the factors that promote the dynamic recrystallization and provide a pathway to control the microstructure and atomic structure by orienting nanoparticles with respect to the impact direction.