Atomistic Study of Hydrogen Effects on Dislocation Mobility and Pile-ups in alpha-Fe
Jun Song (McGill University), W. A. Curtin (EPFL), Shyam Keralavarma (EPFL)
Joint Session: Discrete Dislocation Plasticity and From Atomistics to Reality: Spanning Scales in Simulations and Experiments
Mon 2:40 - 4:00
CIT 227
Atomistic simulations of the effects of H on edge dislocation mobility and pile-ups in alpha-Fe are performed to investigate possible mechanisms for Hydrogen Enhanced Localized Plasticity (HELP) at the nanoscale. Results show that H forms Cottrell atmospheres around moving dislocations, leading to a resistance to dislocation motion via solute drag. Furthermore, the H Cottrell atmospheres do not affect the equilibrium configuration of pile-ups, consistent with conclusions from previous continuum calculations. These results provide no evidence for H-enhanced softening of the plastic flow stress due to mobility effects or modifications to dislocation-dislocation interactions, both of which are oft-proposed mechanisms for HELP. TEM observations of changes in dislocation pile-ups in H-charged metals are thus caused by other phenomena, such as H-induced changes to dislocation pinning by other defects. Continuum calculations are also performed to demonstrate that the in-situ TEM observations may as well be caused by TEM sample swelling during H charging rather by direct H/dislocation phenomena. Our results show that a concise mechanistic understanding of HELP phenomena thus requires evaluation of more complex H/dislocation interactions and further experimental observations.