First-principles calculations of grain boundary cohesive energy, 2; Hydrogen embrittlement of iron

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

It is not known in detail how much hydrogen atoms can be trapped in grain boundaries of metals and how much the cohesive energy (work of fracture) of grain boundary is decreased by the hydrogen trapping. From first-principles, we calculated the trapping energy of hydrogen atoms in bcc Fe Sigma 3 (111) symmetrical tilt grain boundaries and on the fracture surfaces with varying the trapping density of hydrogen. We find that hydrogen atoms can be trapped up to a high concentration in the grain boundaries and on the fracture surfaces for Fe. We also find that the trapping energy on the surface is significantly larger than that in the grain boundary. The cohesive energy of the grain boundary is decreased by hydrogen trapping by about 30% at most. Moreover, the cohesive energy can be decreased by about 70% at most if hydrogen in solid solution state moves quickly and then adsorbs onto the newly generated fracture surfaces.