The effect of B, N and O impurities placed in interstitial and substitutional positions at symmetric Σ5(210) Fe grain boundary was studied by means of first principles calculations. Full relaxation of super-cell shape and volume was applied which resulted in stable asymmetric grain boundaries, depending upon the impurity and its position. In all cases the big shifts (0.47 to 2.33Å) of grains with respect to each other were observed. The equilibrium distance between the grains was decreased for impurities in substitutional positions, and increased for atoms in interstitial sites, compared to the relaxed clean grain boundary. It was found that N in both interstitial and substitutional positions, and B in substitutional position, enhanced cohesion while O in both positions, and interstitial B, were embrittlers. The magnetic moments of Fe atoms at clean grain boundary were remarkably increased compared to the bulk. They tend to the bulk value in the middle of the grain in an oscillatory way.

Effect of Impurities on Grain Boundary Cohesion in BCC Iron. E.Wachowicz, A.Kiejna: Computational Materials Science, 2008, 43[4], 736-43