EFFECTS OF SULFUR AND CARBON ON THE ELECTRONIC STRUCTURE AND BONDING OF A GRAIN BOUNDARY IN α-IRON
Abstract
The electronic structure of a grain boundary (GB) in α-Fe with segregated S and C impurity atoms was calculated by the atom superposition and electron delocalization molecular orbital (ASED-MO) theory. An Fe176 cluster model was used to simulate the local environment of the Σ5 (013), 36.9° [100] tilt boundary.
The results show a site competition on the GB between S and C. The C drives the S away from the boundaries. The C segregation is 4.77 eV more favorable than the S segregation.
Both interstitials weaken Fe–Fe bonds perpendicular to the GB plane and simultaneously form new interstitial-Fe bonds, although C presents the possibility of connecting the two halves of the crystal with a bridge Fe–C–Fe bond. These results should be important for understanding the complex mechanism for decohesion α-Fe.
