First-principles study on the grain boundary embrittlement of metals by solute segregation, 2; Metal(Fe, Al, Cu)-Hydrogen (H) systems

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

The microscopic mechanism of grain boundary embrittlement in metals by hydrogen trapping (segregation) has been not well understood for many years. From first-principles calculations, we show here that the calculated cohesive energy of bcc Fe 3(111) and fcc Al(Cu) 5(012) symmetrical tilt grain boundaries with varying the trapping density of hydrogen can be significantly reduced by hydrogen trapping; it indicates that the reduction of the cohesive energy of the grain boundary may cause the hydrogen-induced grain-boundary embrittlement in Fe, Al, and Cu, although the possibility of hydrogen trapping at grain boundary is very different among those metals. Considering the "mobile" effect of hydrogen during fracture, more hydrogen atoms coming from solid solution state can be trapped on the gradually formed two fracture surfaces in addition to the already trapped "immobile" hydrogen atoms at the grain boundary before fracture.