Formation of refined grains below 10 nm in size and nanoscale interlocking in the particle-particle interfacial regions of cold sprayed pure aluminum

It has been a long-standing challenge to obtain nanocrystalline pure aluminum with grain sizes below 10 nm by plastic deformation. Here, we studied the microstructure characteristics of two bonded pure aluminum powder particles after a cold spray process. In the particle-particle bonding region, nanometersized grains are revealed, about 30% of which are below 10 nm in size. In the particle-particle interface, we observe nanoscale perturbations with interlocking features assisting mechanical bonding. The formation of nanoscale grains and interlocking features is attributed to the extremely high strain and strain rate combined with shear instability in the cold spray process. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.