Hydrogen blistering is known as one type of hydrogen damage to induce the formation ofsubsurface planar cavities and cracks, which shorten the fatigue life of metallic materials.Nevertheless, due to the limitation of the technique, the initaition location of the blisters are stillunclear. Grain boundaries (GBs), as the most common trapping sites of hydrogen, were sensitiveto the generation of hydrogen blisters. Small cavities and holes, which were believed to be thestarting of the blisters, were found on GBs in many pure materials. Type of GBs is decisive when itcomes to the sensitivity to hydrogen embrittlement. In this paper, The effects of GBs on theinitiation of the blisters are studied by synchrotron polychromatic X-ray Laue nano-diffraction (XND)method combing the Molecular dynamics simulations. XND is a cutting-edge technique thatprovides accurate nformations on orientation, mirco strain/stress, dislocation density etc. Thefocused beam size can be as small as 80×80nm~2. Due to the high penetration feature of the X-ray,the technique is non-destructive to the sample and requires little on the sureface conditions of thesamples, which makes it perfect to the study of the blisters.In this paper, GBs effects on initiation of hydrogen-induced blisters in pure iron were investigatedusing XND. Random GBs were more susceptible to blistering than coincidence site lattice GBs. Acomplex deformation mechanism and high strain levels were observed around random GBs.Molecular dynamics simulations revealed that hydrogen induces high stress/strain on random GBs,causing localized plastic deformation. A possible mechanism of blisters formation is proposed.Hydrogen atoms trapped by the free volume of random GBs recombine into hydrogen molecules,causing localized stress and plasticity, enlarging the excess volume of the GBs to eventuallynucleate blisters.
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