Study the atomistic structure of monatomic vanadium under different cooling rates by molecular dynamics simulation

Abstract

We performed molecular dynamics (MD) simulations with the LAMMPS code in order to understand the rapid solidified processes of refractory body-centered-cubic (BCC) metals V under five different cooling rates (γ1 = 1 × 1011K/s, γ2 = 1 × 1012K/s, γ3 = 1 × 1013K/s, γ4 = 5 × 1013K/s, γ5 = 1 × 1014K/s). It is found that the evolution of energy, volume and density of V are strongly dependents on the cooling rates during the rapid solidification. By analyzing the Abraham-Wendt parameter, discovering the magnitudes of the first minimum and maximum of the radial distribution function (RDF) are more effective parameters for specifying the phase boundary between liquid and super-cooled liquid. Compared to the initial crystallizing occurred in the interface with linked atom chain, the growth model of vitrification is presented through icosahedral medium-range orders (IMROs) with shell structure cored by isolated icosahedra. Further analyzing the variation of the number of icosahedra (ICO), hexagonal-close-packed (HCP), face-centered-cubic (FCC) and BCC clusters as a function of temperature by polyhedral template matching method (PTMM), it is found that the variation of tracking clusters not only occurs in the liquid and super-cooled liquid, but also exist in low temperature region (below the crystallization temperature (Tc) or glass transition temperature (Tg)), which breaks through our previous understanding for the evolution of clusters should only in high temperature region rather than in lower temperature region. In addition, both of the evolution of the density field for crystal and non-crystal exhibited obviously non-homogeneous, which maybe lead to non-uniformity of nucleation and vitrification in some degree, respectively.