Molecular dynamics simulation of microstructure and atom-level mechanism of crystallization pathway in iron nanoparticle

Abstract

Abstract We use the molecular dynamics simulation to study iron nanoparticles (NP) which consist of 5000 atoms at temperatures of 450 and 850 K. The crystallization and structure evolution was analyzed through pair radial distribution function, transition to different x-types, with x is the bcc, fcc and hcp, ico, 14, 12, and dynamical structure parameters. Simulation results that at 450 K, NP contains a large number of ico-type atoms which play a role in preventing of crystallization. The crystallization happened when NP was annealed at 850 K for 40 ns. Transitions to bcc-type do not happen arbitrarily at any location in NP, but instead they are focused in a non-equilibrium region. We showed that the crystallization pathway includes intermediate states between amorphous and crystalline phases. Firstly, a large cluster of cryst-atom is formed in a middle layer of NP. Next, this cluster grows up and the parameter for this cluster increases rapidly. Finally, the cluster of cryst-atom is located in a well-equilibrium region covered a major part of NP. The structure of crystalline NP is strongly heterogeneous and consists of separate local structure regions.