| Summary: | 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. © 2021 The Author(s). Published by Elsevier Ltd on behalf of Acta Materialia Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Received 31 May 2021, Revised 28 June 2021, Accepted 28 June 2021, Available online 14 July 2021. Y.D. acknowledge the financial support provided by the Research Council of Norway under the M-HEAT project (Grant No. 294689). All simulations are carried out on the Fram (Grant No. NN9110K, NN9391K) high-performance computer clusters at NTNU, Trondheim, and Stallo at UiT, Tromsø. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Published - 1-s2.0-S1359646221004024-main.pdf Supplemental Material - 1-s2.0-S1359646221004024-mmc1.mp4
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