Comparison of site preferences of 57Co at grain boundaries in Fe-Si and Fe-Al alloys

Emission Moessbauer spectroscopy was applied to the study of grain boundaries in the polycrystalline samples of iron rich Fe-Al and Fe-Si alloys. The results obtained on Fe-Al samples indicate complicated phase and chemical composition along grain boundaries (GBs). Neither homogeneous increase in Al concentration at GBs nor important site preference of Co atoms is observed. A large fraction of Co atoms occupy positions of lower symmetry. The results on Fe-Si show differencies in the chemical composition in grain interiors (GIs) and at GBs. An increase in Si concentration at GBs is observed there. In Fe-! & at.%Si sample a strong site preference of cobalt atoms at GBs is detected. The diffusing Co atoms prefer the lattice sites, which are expected to be occupied by structural vacancies in the D03 superstructure