Influence of bulk composition on grain boundary segregation in B2Fe-Al:: An atomic-scale simulation study -: art. no. 174105

The atomic structure of the (310)[001] symmetrical tilt grain boundary (GB) in B2 Fe-Al ordered alloys was studied at T = 0 K by numerical simulations using N-body empirical potentials. As expected from the high degree of order of B2 Fe-Al the coincidence site lattice (CSL) theory is found a relevant approximation for GB crystallography, the stable GB variants being close to the usual symmetric and pseudosymmetric CSL models, with no GB vacancies. However, as regards GB chemistry, the extension to interfaces of the independent point defect approximation, rigorous for bulk ordered compounds, and assessment of its validity by a full treatment of interactions between GB point defects reveal a strong dependence of GB properties on alloy off-stoichiometry: single-layer Fe segregation holds in Fe-rich Fe-Al, whereas in Al-rich alloys, a complex multilayer Al segregation appears, with the possibility of a GB phase transition, and GB glide weakly dependent on GB chemistry seems easy in the [001] direction. These elements may help explain the experimentally well-known high dependence of the mechanical properties of B2 Fe-Al on bulk composition.