First-principles study of the grain-boundary embrittlement of metals

Yamaguchi, Masatake   ; Ebihara, Kenichi   ; Itakura, Mitsuhiro  ; Suzudo, Tomoaki   ; Kaburaki, Hideo

It is not known in detail how much solute atoms segregate in grain boundaries of metals and how much the cohesive energy (work of fracture) of grain boundary is decreased by the segregation. From first-principles, we calculated the segregation energy of some solute elements like boron (B), carbon (C), phosphorous (P), and sulfur (S) in bcc Fe Sigma 3 (111) symmetrical tilt grain boundary with varying the segregation density. We find that these elements can segregate up to a high concentration in the grain boundary. We also find that the segregation energy on the fracture surface is significantly larger than that in the grain boundary for the embrittling elements like P and S. On the contrary, the cohesive energy is increased by B and C segregation. The increase-decrease rate in the calculated cohesive energy by solute segregation is found to be well correlated with experimentally observed shift in ductile-to-brittle transition temperature by solute segregation.