First-principles study in Fe grain boundary with Al segregation: variation in electronic structures with straining

First-principles fully relaxed tensile tests were performed on a sigma 3 (111)/[10] tilt Fe grain boundary (GB) segregated with Al. The effects of Al segregation on bond breaking in the GB were compared with those of Cu and P, which are typical GB embrittlers because of charge transfer and covalent-like characteristics, respectively. It was suggested by first-principles tensile tests that the intergranular embrittling potency of Al is as strong as that of Cu. However, this result disagreed with an estimation based on the Rice-Wang thermodynamic model. The first bond breaking site in the Al-segregated GB was the Fe-Fe bond neighbouring the Al atom, as in the Cu-segregated GB. This is typical of bond breaking due to charge transfer. However, no charge transfer was observed from the Fe atom to the Al atom, while the Fe atom neighbouring the Al atom showed covalent-like characteristics. It was suggested from investigations of the charge density at the bond critical point that the effect of covalent-like characteristics of Al on the Fe-Fe bond was small in the initial stage of straining, but it increased as the charge density of the Fe-Fe bond decreased with increasing strain. The investigation of the dynamic change in electronic structure also shed light on the difference of bond breaking behaviour in metallic and covalent-like bonding in metallic materials.