Homogeneous Nucleation and Inner Structure Evolution in Nucleus Fe from Classic Molecular Dynamics Simulation

Molecular dynamic simulation was used to study the solidification process of liquid Fe with Sutton-Chen potential. Bond orientational order (BOO) parameters and Voronoi polyhedron index (VPI) method, named BOO+VPI method, were applied to identify atomic local structure and local volume precisely. During the solidification process, two large clusters were detected, one is an imperfect five-fold twinning structure, and the other is a lamellar structure. In addition, the density and order of the two clusters were analyzed along with their growth. All analyses suggest that the density and the order of the crystal nucleus increase gradually with the increase of the size, and the order of the crystal nucleus with the five-fold twinning structure is higher. Meanwhile, the embryos are always found in high structure-ordered region instead of high density region.