Shock-induced plastic deformation of nanopowder Ti during consolidation and spallation.

Consolidating nanopowder metals via impact loading is a potentially significant method for synthesizing and processing bulk nanocrystalline materials. However, until now, the microstructural features, plastic deformation during consolidation, and corresponding mechanisms have been seldom revealed. Using molecular dynamics (MD) simulations, we have studied the plastic deformation, densification, spallation, and micro-jetting in nanopowder titanium (np-Ti) during shock. Upon impact, np-Ti undergoes a transition from heterogeneous plasticity, including basal stacking faults (SFs) and {101̄2} twinning, to homogeneous disordering, as the impact velocity increases. Then the nanopowder structure evolves into a bulk nanostructure after the final densification, contributed by pore collapse. The subsequent detwinning arises during the release and tension stage, conducing to a partial structural recovery. When the impact velocity up ≥ 1.0 km s-1, the spallation is following, prompted via GB-sliding and disordering. Upon shock impact, it also facilitates micro-jetting owing to the presence of nanopores, contributing to the pressure gradient and transverse velocity gradient.