Hydrogen hardening effect in heavily deformed single crystal α-Fe

Molecular dynamics simulations were performed to investigate the hydrogen interaction with edge dislocations during deformation in α-Fe. In particular, uniaxial tensile tests of a single crystal iron were conducted after the single crystal was plastically deformed to introduce high density of edge dislocations and was doped with different levels of lattice hydrogen concentration. During system relaxation, hydrogen atoms have tendency to diffuse and stay around dislocation line – a well-known hydrogen trap-site in α-Fe. Our simulations show that the yield strength of the bcc iron is very sensitive to the presence of hydrogen within edge dislocations, i.e., it increases as hydrogen concentration increases. After yielding, hydrogen atoms are de-associated with the moving dislocations, suggesting that the yield strength enhancement is caused by the hydrogen pinning effect. This direct observation of hydrogen hardening effects has confirmed the experimental findings by Matsui, etc. Additional simulations also indicate that hydrogen interaction with edge dislocations is sensitive to temperature as well as vacancies around dislocation core.