International Hydrogen Conference (IHC 2012): Hydrogen-Materials Interactions
80 Intergranular Decohesion Induced by Mobile Hydrogen in Iron with and without Segregated Carbon: First-Principles Calculations
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The effect of segregated carbon (C) on hydrogen (H)-induced slow and fast cracking along symmetrically tilted Σ3(111) grain boundaries (GBs) of bcc iron has been studied by first-principles calculations, together with the thermodynamic theory of GB decohesion. The atomistic analysis is capable of determining explicitly the coverage dependence of the H segregation energy due to the repulsive interaction among segregated H atoms along GBs with and without a half and full coverage of segregated C and their fracture surfaces (FSs). It was found that the C segregation does not only strengthen the GB but also suppresses the segregation of combined mobile/immobile H atoms along the GB and FSs. Therefore, the combined mobile/immobile H segregation only induces 10-25% reduction in the GB cohesive energy (2γint) for slow cracking along the GB with a half C coverage for a typical range of the bulk hydrogen content of 10-8-10-5 atomic fraction, compared with 30-40% reduction in 2γint along the C-free GB.