Effects of hydrogen on the deformation mechanism of face-centred cubic Fe–C single crystal with nanovoid: A molecular dynamics simulation

Abstract

In the present work, the deformation mechanisms of face-centred cubic (fcc) Fe–C single crystal with nanovoid containing hydrogen at various contents are investigated by molecular dynamics (MD) tensile simulations. The microstructural evolution of the supercell without H reveals that the plastic deformation mechanism is fcc→bcc→hcp continuous martensitic transformation. For the supercell containing 2 at% H, the mechanical response and plastic deformation mechanism are similar to those of the supercell without H. The difference is that bcc martensite nucleation is accompanied by dislocation nucleation, which indicates that a small amount of H addition will promote dislocation slip. When the H content reaches 5 at%, the dislocation slip enhanced by H completely overcomes the martensitic transformation and becomes the main plastic deformation mechanism. By analysing the per-atom potential energy of H atoms and Fe atoms, it is found that the potential energy of H atoms near the dislocation line and on the slip plane will increase, which may reduce the lattice resistance of dislocation slip. Moreover, the addition of H increases the average potential energy of fcc Fe atoms, which results in the reduction in Fe atomic binding, thus increasing the dislocation mobility. The dislocation slip causes localized plasticity on the nanovoid surface, which promotes the expansion of the nanovoid and leads to hydrogen embrittlement. The martensitic transformation and dislocation slip are prone to nucleation at the edge of the nanovoid, which indicates that in practical situations, void defects with sharp corners could induce premature plastic deformation in fcc crystals.