First-principles study on the decohesion of grain boundaries in metals by hydrogen trapping

水素トラップによる金属粒界の凝集エネルギー低下の第一原理計算

山口 正剛   ; 海老原 健一   ; 板倉 充洋  ; 鈴土 知明   ; 蕪木 英雄; 門吉 朋子*

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

第一原理計算を用いて、鉄,アルミ,銅の結晶粒界における水素のトラッピングエネルギーと凝集エネルギーの低下を計算した。鉄やアルミの粒界においては、水素がたくさんトラップされること、銅ではあまりトラップされないことがわかった。また、粒界の凝集エネルギー低下も鉄とアルミで大きく、銅では小さいことなどがわかった。

From first-principles, we calculated the trapping energy of hydrogen atoms in bcc Fe Sigma 3 (111) and fcc Al (Cu) Sigma 5 (012) symmetrical tilt grain boundaries and on the fracture surfaces with varying the trapping density of hydrogen. For Fe case, 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. For Al case, we find a similar trend as Fe case. For Cu case, on the other hand, the decrease in the cohesive energy of the grain boundary by the hydrogen trapping is much smaller than that for Fe and Al cases. This is because the trapping density of hydrogen atoms is very low in the Cu grain boundary and its fracture surface. The hydrogen trapping may cause brittle fracture in the grain boundaries for Fe and Al.