Effect of magnetism on the atomic structure and properties of [formula omitted]5 grain boundaries in fcc Fe and fcc Ni

Abstract

Grain boundaries (GB) play a major role in the mechanical properties of steel. We model here the most common Σ5 (210) and (310) [001] tilt boundaries in fcc Ni and fcc Fe which are main components of steel, paying particular attention to the effect of magnetism on the relative stabilities of the competing GB structures and on their main characteristics (excess volume, microstructure, stress profile, ...). To this aim we develop a new interatomic potential in the second moment approximation of the Tight-Binding scheme which accounts for magnetism in an effective manner in order to relax the structures at T=0K within quenched molecular dynamics simulations. Similar results are obtained for Fe and Ni, even though magnetic effects are found much more important in the former case. More precisely, magnetism significantly lowers the excess GB energy and volume, strongly reduces the stress in the GB region, and can even modify the microstructure in some cases. Finally a local analysis is proposed which allows to classify the relative stabilities of the different structures in terms of only a few given atomic sites.