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 Fe 176 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 .