Crystallization of Amorphous Iron Nanoparticles by Means of Molecular Dynamics Simulation

Method of molecular dynamics (MD) simulation was applied to study the crystallization of the amorphous iron nanoparticles. The research sample is a sphere with a radius of 32.5Å under free boundary conditions. The mechanism of the crystallization occurred due to variation of structure and thermodynamic properties during the entire process. We've found that when the samples were heated to 900K and annealed through 3×106 ÷ 107 MD steps, the crystalline nucleation is formed and grew up; and it leads to a shift from amorphous to crystalline to form bcc structure. Crystalline form consists of two parts: a core with crystalline structure and a surface with amorphous structure. A detailed analysis reveals that the nucleation proceeds in a middle spherical layer. After that the crystal cluster grows firstly forward to the center of nanoparticle, and then it spreads to the surface. In the case when the sample is annealed at 300 K, we found small nuclei nearby the surface of nanoparticle. However, these nuclei cannot grow to a large size and the sample remains amorphous form for long annealing times.