The effects of several metalloid (B), metalloid-like (C, P) and non-metallic impurities (N, O, S) on the structure, energetics and mechanical properties of Σ3(111) and Σ5(210) grain boundaries in ferromagnetic α-Fe were studied from first principles. For two different concentrations and positions of impurity atoms, the variations in grain-boundary properties were analysed. Most of the impurities enhance the relaxation of the interplanar spacing of the pure grains. Interstitial impurities at both grain boundaries were shown to increase the separation of the grains while substitutional ones in general either do not alter or decrease the grains' separation. It was shown that at the Σ5 grain boundary, for all impurity atoms considered, the positions in the boundary layer were energetically favoured independently of the interstitial or substitutional site, whereas the enrichment of the Σ3 grain boundary was favoured for the impurities of the interstitial sites as well as for a substitutional P and C. It was found that, in most cases, impurity atoms both in interstitial and substitutional positions at grain boundaries acted as embrittlers. Interstitial B, P and C strengthened the Σ3 grain-boundary cohesion, and B and C at lower concentrations strengthened the Σ5 GB. All substitutional impurities, except for B, weakened the grain boundaries. The magnetic moments on the impurities were very small and in most cases aligned anti-parallel to the moments on the neighbouring Fe atoms.

Effect of Impurities on Structural, Cohesive and Magnetic Properties of Grain Boundaries in α-Fe. E.Wachowicz, A.Kiejna: Modelling and Simulation in Materials Science and Engineering, 2011, 19[2], 025001