Abstract
It is known that hydrogen can influence the dislocation plasticity and fracture mode transition of metallic materials, however, the nanoscale interaction mechanism between hydrogen and grain boundary largely remains illusive. By uniaxial straining of bi-crystalline Ni with a Σ5(210)[001] grain boundary, a transgranular to intergranular fracture transition facilitated by hydrogen is elucidated by atomistic modeling, and a specific hydrogen-controlled plasticity mechanism is revealed. Hydrogen is found to form a local atmosphere in the vicinity of grain boundary, which induces a local stress concentration and inhibits the subsequent stress relaxation at the grain boundary during deformation. It is this local stress concentration that promotes earlier dislocation emission, twinning evolution, and generation of more vacancies that facilitate nanovoiding. The nucleation and growth of nanovoids finally leads to intergranular fracture at the grain boundary, in contrast to the transgranular fracture of hydrogen-free sample.
Highlights
It is known that hydrogen can influence the dislocation plasticity and fracture mode transition of metallic materials, the nanoscale interaction mechanism between hydrogen and grain boundary largely remains illusive
All the studies [8,9,10,11,12,13,14,15,16] show that grain boundary (GB) plays an important role in hydrogen embrittlement (HE) and the hydrogen-GB interactions hold the key to understanding the transgranular to intergranular fracture transition
H at crack tips could contribute to the weakening of metal bonds resulting in fracture, but it does not make an explanation for the enhanced plasticity
Summary
It is known that hydrogen can influence the dislocation plasticity and fracture mode transition of metallic materials, the nanoscale interaction mechanism between hydrogen and grain boundary largely remains illusive. All the studies [8,9,10,11,12,13,14,15,16] show that grain boundary (GB) plays an important role in HE and the hydrogen-GB interactions hold the key to understanding the transgranular to intergranular fracture transition. HESIV [28,29,30,31,32] assumes that the vacancy clusters generated during plastic deformation are stabilized by forming H-vacancy complexes, which will further interact with the dislocations.
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