N-body interatomic potential for molecular dynamics simulations of V-Cr-Nb-Mo-Ta-W system

Abstract

Diffusion in high-entropy alloys is an important phenomenon controlling its evolution during exploitation. Its detailed investigation, especially at elevated temperatures, is a challenging task. Molecular dynamics simulations facilitate significantly findings in this area and provide valuable insights into it. The key part of the molecular dynamics is the interatomic potential representing the dependence of the potential energy of the system of atoms on their coordinates. To correctly calculate the diffusivity, the potentials should satisfy several criteria such as an accurate reproduction of the melting point and thermal expansion. The last one is crucial as diffusion is strongly influenced by the size factor. We used the N-body approach to construct the interatomic potential for the high-entropy alloy V-Cr-Nb-Mo-Ta-W system, which consists of the potentials for pure elements and binary systems constituting the six-component one. The constituting potentials reproduce structure, elastic, defect and melting properties of pure elements and concentration dependent properties of binary systems. As a test for the VNbMoTaW and VCrNbMoTaW alloys, we calculated the forces acting on atoms for a set of different compositions and obtained the adequate agreement with the density functional theory (DFT) results. Additionally, we computed the surface and excess screw dislocation energies for both pure elements and alloys. The experimental surface energy values averaged over the elements show remarkable agreement (less than 10%) for the equiatomic VNbMoTaW and VCrNbMoTaW alloys. The excess screw dislocation energies of pure elements are predicted in qualitative agreement with DFT results, with tungsten having the highest energy and vanadium and niobium having the lowest. The corresponding values for five- and six-component alloys are less than DFT ones with deviations of 7% and 34%, respectively. They are close or moderately less than the energies averaged over pure elements.