The key role played by dislocation core radius and energy in hydrogen interaction with dislocations

It is generally believed that the H-induced reduction in dislocation energy plays a key role in modifying dislocation behaviors in the process of hydrogen embrittlement. Here, we examine the factors that lead to H reducing the line energies of the edge and screw dislocations in bcc Fe by atomistic simulations. Grand canonical Monte Carlo simulations are conducted to obtain the distribution of H around the dislocations. We find that H mainly aggregates at the dislocation cores and the H concentration in the elastic field of dislocations is extremely low. The direct consequences of such a distribution pattern of H are as follows. (i) In contrast with previous studies, H induces no change in the shear modulus of the systems containing dislocations. (ii) H increases the core radii and decreases the core energies of the dislocations, which are the only factors leading to the reduction of dislocation line energy by H. (iii) H brings little effect on the stress field of either the edge or screw dislocation, implying that H induces almost no stress-shielding effect on dislocations. A linear relation between the critical shear stress for homogeneous dislocation nucleation and logarithmic bulk H concentration is thus revealed, based on the atomistic result of the H-induced increase in the core radius and decrease in the core energy of the dislocations. The present results indicate that the dislocation-dislocation interaction in the presence of H, which is the key ingredient for the H-enhanced localized plasticity mechanism for hydrogen embrittlement, can be easily evaluated by the linear elastic theory of dislocations if the core radius and energy of dislocations are properly described. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.