Evolution of local atomic structure during solidification of U116Nb12 liquid: An ab initio molecular dynamics study

Abstract

By means of ab initio molecular dynamics (AIMD), the evolution of local atomic structures of the U116Nb12 liquid alloy during solidification from 2600 K to 600 K was systemically investigated in terms of the pair correlation function, structure factor, bond angle distribution, coordination number, the Honeycutt-Anderson (HA) and Voronoi index as well as diffusivity and viscosity. The distinctly linear dependence of the mean square displacements (MSDs) as a function of time indicates that the equilibrium configurations are derived from our AIMD simulations. The equations of the volumetric expansion, thermal diffusion and viscosity of the U116Nb12 liquid alloy are presented, respectively. The most abundant structures in the U116Nb12 liquid alloy are those having HA indices of 1551, 1541, 1431, 1441 and 1661. The Voronoi analysis reveals that the distributions of local atomic structures at high temperature are homogeneous, whereas Voronoi polyhedra trend to form <0,2,8,2>, <0,0,12,0>, <0,1,10,2>, <0,1,10,3>, <0,2,8,4>, <0,3,6,5> and <0,3,8,3> with the larger fraction at low temperature. The analysis of chemical short-range order and structural properties suggests that the icosahedra and bcc-type clusters play the dominant roles upon cooling and, the addition of Nb in the U116Nb12 liquid alloy is indeed beneficial to occurrence of the local atomic structural evolution.