Effects of H segregation on shear-coupled motion of < 110 > grain boundaries in alpha-fe
JQ Li and C Lu and LQ Pei and C Zhang and R Wang and K Tieu, INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 44, 18616-18627 (2019).
By using large-scale molecular dynamics (MD) simulations, the influence of solute hydrogen (H) segregation into several typical 1 (1) over bar0 symmetric tilt grain boundaries (STGBs) on the shear response and coupled grain boundary (GB) migration of bicrystals in alpha-Fe is systematically examined. Depending on our geometric model of coupling for 1 (1) over bar0 STGBs in body-centred cubic (BCC) metals, two different coupling branches (<100> and <111>) are predicted and further validated by the MD results. Our atomistic simulations show that solute H atoms impede coupled GB motion irrespective of the GB structure, which mainly stems from the fact that H considerably modifies the local atomic structures of the GBs. At high H concentrations, the response of GBs to shear deformation changes from GB coupling to pure GB sliding. In addition, it is found that H can facilitate the vacancy generation via enhancing the interaction of GB dislocations within the framework of the H-enhanced localized plasticity (HELP) mechanism. Although H-vacancy clusters are formed by solute H combining with nucleated vacancies, they cannot grow larger owing to the migration of GBs with extensive dislocation plasticity. This directly prevents the occurrence of H embrittlement (HE). These findings deepen our overall understanding of the role of solute H in GB-mediated plasticity process (GB migration) of metallic materials and provide a possible path to designing new materials with high resistance to HE. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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