Ab initio and atomistic study of generalized stacking fault energies in Mg and Mg–Y alloys

Z Pei,L-F Zhu,H W Sheng,S Zaefferer,M Friák,C P Race,J Neugebauer,J Von Pezold,D Raabe,S Sandlöbes,B Svendsen

doi:10.1088/1367-2630/15/4/043020

Abstract

Magnesium–yttrium alloys show significantly improved room temperature ductility when compared with pure Mg. We study this interesting phenomenon theoretically at the atomic scale employing quantum-mechanical (so-called ab initio) and atomistic modeling methods. Specifically, we have calculated generalized stacking fault energies for five slip systems in both elemental magnesium (Mg) and Mg–Y alloys using (i) density functional theory and (ii) a set of embedded-atom-method (EAM) potentials. These calculations predict that the addition of yttrium results in a reduction in the unstable stacking fault energy of basal slip systems. Specifically in the case of an I2 stacking fault, the predicted reduction of the stacking fault energy due to Y atoms was verified by experimental measurements. We find a similar reduction for the stable stacking fault energy of the non-basal slip system. On the other hand, other energies along this particular γ-surface profile increase with the addition of Y. In parallel to our quantum-mechanical calculations, we have also developed a new EAM Mg–Y potential and thoroughly tested its performance. The comparison of quantum-mechanical and atomistic results indicates that the new potential is suitable for future large-scale atomistic simulations.

Highlights

IntroductionIt was shown, for example, that maxima occurring along GSFE profiles, so-called unstable stacking fault energies (USFEs), determine the behavior of slip modes and the ductility in fcc metals [18]
Our study is motivated by the fact that rather little is known about GSFEs in Mg–Y alloys, especially in the case of non-basal deformation modes
Using DFT and newly developed EAM potentials, we present GSFE profiles for five selected slip systems in both pure Mg and Mg–Y alloys

Summary

Introduction

It was shown, for example, that maxima occurring along GSFE profiles, so-called unstable stacking fault energies (USFEs), determine the behavior of slip modes and the ductility in fcc metals [18]. As processes related to the plasticity of materials typically span over much larger scales, methods based on inter-atomic potentials are often used instead. For these simulations, well-tested and reliable potentials are necessary. Slip deformation modes can be studied by calculating generalized stacking fault energies, known as γ -surfaces [12]. For the minimization after each incremental shift, atomic positions are constrained along the lateral dimensions of the glide plane, but atoms can reduce the total energy of the system by relaxing in the direction perpendicular to the studied glide plane

Objectives

Results

Conclusion