The correlation between chemical effect and segregation behavior in metallic Al liquid

Abstract

In this work, a study of melt Al1−xMx alloys was carried out by ab initio molecular dynamics (AIMD) simulation within GGA and LDA. Two groups of typical elements Fe, Co, Ni and Cr, V, Ti, showing opposite segregation behaviors in metallic liquid Al, were chosen as the solutes M. The short-range orders (SROs) were analyzed based on the calculation of the static structure factor, pair-correlation function, common neighbor analysis, bond angle distribution function (BADF) and Voronoi polyhedron (VP) analysis. The affinity between unlike species in molten Al1-xMx divides into two groups according to the segregation tendency. The solute atoms with distribution coefficient smaller than 1 (k < 1) prefer to bond with heterogeneous atoms and tend to form medium-range order (MRO) in sharing of common Al atoms, while the solute atoms with distribution coefficient smaller than 1 (k > 1) tend to bond with homogeneous atoms directly. The abundant Voronoi polyhedron (VP) using the solute atom with k < 1 as centered atom is crystal-like cluster (〈0,3,6,0〉 and 〈0,3,6,1〉), whereas that using the solute atom with k > 1 as centered atom is mixed cluster (〈0,2,8,1〉 or 〈0,2,8,2〉). The difference of VP around different solute atoms is mainly caused by the diversity of fraction of different types of bonded pairs of various solute atoms. Our results exhibit that there indeed exist the correlations between the segregation behavior of solutes and the chemical effects in the Al melt. The diffusion of solute elements is not closely related to segregation. This paper also illustrates that the simulations within GGA or LDA yield similar results except for the minor difference. Our work sheds light on the segregation nature of typical solutes from a structural perspective.