Bonding processes during the dynamic compaction of metallic powders

Abstract

The microstructures of a range of metallic powder compacts obtained by dynamic, or shock wave, compaction have been examined in an attempt to elucidate the processes leading to bonding. Strain localization around the particle exteriors leads to extensive surface shear, adiabatic heating and eventually, perhaps, melting. Regions of interparticle bonding, and non-bonding, have been identified. Three classes of bond region have been seen: a heavily deformed and recovered or recrystallized region containing elongated subgrains; a region where melting occurred and columnar grains were produced by subsequent solidification; a region where molten material, produced elsewhere by deformation and adiabatic heating and squeezed to the new location during the dynamic processing, was very rapidly solidified to produce an equiaxed microcrystalline structure. These three regions bear resemblance to those structures observed in explosively bonded joints and imply that essentially the same mechanisms are occurring during the two processes.