Dynamic compaction of aluminum nanocrystals

We investigated shock-compaction behavior of nanocrystalline aluminum (n-Al) powder with an average particle size of about 50-70 nm. The starting powders were analyzed using various analytical tools, including transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The initial Al particles were found to be coated naturally by a uniform, thin (similar to 5 nm) near-stoichiometric, amorphous oxide layer. Shock compaction was carried out at 2-3 GPa (20-30 kbars) to obtain high-density disks. The microstructure of samples prior to and after consolidation were both examined. Despite substantial deformation during dynamic compaction, the surface oxide remained intact at the pressures employed and prevented a metallurgical bond between the nano-sized particles. Theoretical simulations of the dynamic compaction of n-Al were also carried out using an Eulerian hydrocode. The results were in good agreement with experimental observations. Copyright (C) 1996 Acta Metallurgica Inc.