The crystal structures of sintered copper nanoparticles: A molecular dynamics study

The coalescence of nano-crystals during sintering is often found to result in interesting crystalline structures such as multi-fold twins, and yet the plasticity mechanism accompanying their formation is unclear. In this work, the sintering behavior of two unsupported copper nanoparticles initially at room temperature is investigated by molecular dynamics simulations under the constant-energy ensemble. The results reveal that once the two nanoparticles are brought into contact, they often go through drastic structural changes with the inter-particle grain boundary quickly eliminated, and single- and multi-fold twinning occurs frequently in the coalesced product. Whereas the formation of single twins is found to be via the more usual mechanism of emission of Shockley partials on {1 1 1} planes, the formation of fivefold twins, however, takes place via a novel dislocation-free mechanism involving a series of shear and rigid-body rotation processes caused by elastic waves with amplitudes not corresponding to any allowable Burgers vector in the fcc lattice. Such a lattice-wave, dislocation-free twinning mechanism has never been reported before.

► The sintering of Cu nanocrystals is simulated by MD at room temperature.
► Two contacting particles can quickly transform into a single- or multi-fold twinned particle.
► Single twins are formed by Shockley partial dislocations.
► Fivefold twins are formed by a dislocation-free elastic-wave mechanism unseen before.
► Plasticity mechanisms in nano-sized crystals can be completely different from those in bulk.