The ASED-MO theory was used to study the effects of H and the H-C and H-B pairs in the electronic structure of a Fe grain boundary. The results obtained for H in a grain boundary model were consistent with its behavior as a chemical embrittler. The total energies calculated for FeH, FeC and FeB clusters indicated that all interstitials segregate to the grain boundary. C has the lowest energy, followed by B, and could compete with other impurities for the site location on the grain boundary. The results obtained for FeCH and FeBH were consistent with the observed behavior of C and B as cohesion enhancers. A strong repulsive interaction between C and H and B and H atoms was developed if they occupy the nearest interstitial site on the grain boundary. When C or B were present, the total energies were similar to that obtained for the FeH cluster. This indicated that H was displaced from the capped trigonal prism. Also, no C-H or B-H interaction was detected. Density of states and crystal orbital overlap population curves were used to shed more light on the interstitial-Fe grain boundary interaction. The existence of strong metal–metalloid bonds was shown, which were primarily due to Fe 3d, 4s and C (or B) 2s, 2p interactions.

Segregation of H, C and B to Σ = 5 (013) α-Fe Grain Boundary – a Theoretical Study. S.Gesari, B.Irigoyen, A.Juan: Applied Surface Science, 2006, 253[4], 1939-45