Cohesive and magnetic properties of grain boundaries in bcc Fe with Cr additions

TL;DR

This study uses first-principles calculations to analyze how chromium additions affect the structural, cohesive, and magnetic properties of grain boundaries in bcc iron, revealing enhanced cohesion and magnetic moment variations.

Contribution

It provides new insights into the effects of Cr solutes on grain boundary cohesion and magnetism in bcc Fe, considering different concentrations and positions of Cr atoms.

Findings

Cr atoms in GB interstices increase cohesion by 0.5-1.2 J/m$^2$

Cr in boundary layers enhances cohesion by 0.5 J/m$^2$

Cr impurities segregate to grain boundaries in Fe

Abstract

Structural, cohesive, and magnetic properties of two symmetric $\Sigma3(111)$ and $\Sigma5(210)$ tilt grain boundaries (GBs) in pure bcc Fe and in dilute FeCr alloys are studied from first principles. Different concentration and position of Cr solute atoms are considered. We found that Cr atoms placed in the GB interstice enhance the cohesion by 0.5-1.2 J/m$^2$. Substitutional Cr in the layers adjacent to the boundary shows anisotropic effect on the GB cohesion: it is neutral when placed in the (111) oriented Fe grains, and enhances cohesion (by 0.5 J/m$^2$) when substituted in the boundary layer of the (210) grains. The strengthening effect of the Cr solute is dominated by the chemical component of the adhesive binding energy. Our calculations show that unlike the free iron surfaces, Cr impurities segregate to the boundaries of the Fe grains. The magnetic moments on GB atoms are substantially changed and their variation correlates with the corresponding relaxation pattern of the GB planes. The moments on Cr additions are 2-4 times enhanced in comparison with that in a Cr crystal and are antiparallel to the moments on the Fe atoms.