Shock-induced consolidation and spallation of Cu nanopowders

Abstract

A useful synthesis technique, shock synthesis of bulk nanomaterials from nanopowders, is explored here with molecular dynamics simulations. We choose nanoporous Cu (∼11 nm in grain size and 6% porosity) as a representative system, and perform consolidation and spallation simulations. The spallation simulations characterize the consolidated nanopowders in terms of spall strength and damage mechanisms. The impactor is full density Cu, and the impact velocity (ui) ranges from 0.2 to 2 km s−1. We present detailed analysis of consolidation and spallation processes, including atomic-level structure and wave propagation features. The critical values of ui are identified for the onset plasticity at the contact points (0.2 km s−1) and complete void collapse (0.5 km s−1). Void collapse involves dislocations, lattice rotation, shearing/friction, heating, and microkinetic energy. Plasticity initiated at the contact points and its propagation play a key role in void collapse at low ui, while the pronounced, grain-wise deformation may contribute as well at high ui. The grain structure gives rise to nonplanar shock response at nanometer scales. Bulk nanomaterials from ultrafine nanopowders (∼10 nm) can be synthesized with shock waves. For spallation, grain boundary (GB) or GB triple junction damage prevails, while we also observe intragranular voids as a result of GB plasticity.