EFFECT OF SULPHUR AND CARBON SEGREGATION ON CHEMICAL BONDING OF GRAIN BOUNDARIES IN BCC METAL IRON

The effect of sulphur and carbon impurity segregation on chemical bonding of grain boundaries for b.c.c. metal iron was investigated using the self-consistent field X_α discrete variational method. A relaxed trigonal-prism cluster was used as one of the structural units of the grain boundaries. The grain boundary embrittlement, which is caused by impurity segregation, is interpreted by the electron charge transfer from neighbouring iron atoms onto impurity atoms, and by the characteristics of empty levels in the energy bands of the segregated grain boundaries.