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Report No.

Mobile effect of hydrogen on intergranular decohesion of iron; First-principles calculations

Yamaguchi, Masatake  ; Kameda, Jun*; Ebihara, Kenichi; Itakura, Mitsuhiro; Kaburaki, Hideo

Atomistic mechanisms of hydrogen-induced cracking along a bcc Fe $$Sigma 3(111)$$ symmetrical tilt grain boundary (GB) have been studied by first-principles calculations. The mobile and immobile effects of hydrogen on the GB decohesion are analyzed by calculating the dependence of hydrogen segregation energy on the coverage relevant to the repulsive interaction among segregated hydrogen atoms at the GB and on its fracture surfaces, together with generalizing McLean's formula. It was found that the segregation of combined mobile and immobile hydrogen atoms from the bulk and/or GB on the fracture surfaces causes much stronger reduction (70-80%) in the GB cohesive energy. It can occur even at a very low bulk hydrogen content of about 10$$^{-9}$$ atomic fraction during slow cracking. This is in contrast with only 10-20% decohesion induced by immobile hydrogen at much higher hydrogen content during fast cracking.



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Category:Materials Science, Multidisciplinary



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