Solute Hydrogen Effects on the Uniaxial Tension Response of Polycrystalline α-Fe by Molecular Dynamics Simulation

The premature fracture failure of polycrystalline α-Fe poses lots of hidden safety problems due to hydrogen absorption during human activities. A key challenge for the failure process is understanding the effects of hydrogen on grain boundaries (GBs). The study here demonstrates that the rapid diffusion of hydrogen leads to the formation of hydrogen-induced defects in a very short time. Specifically, hydrogen segregation results in void formation and even aggregation at GBs, which plays a critical role in crack initiation and propagation. The mechanical response of GBs with varying hydrogen levels is investigated using large-scale molecular dynamics (MD) simulations. The analysis shows that hydrogen increases the yield stress, thereby inhibiting dislocation emission from GBs. Additionally, GB damage alters the fracture mode from a mix of intergranular and intragranular fracture without hydrogen to a fully intergranular fracture with multi-site crack nucleation at high hydrogen concentrations (e.g., Ch = 3 at.%). This shift is driven by hydrogen-induced void formation at GBs and hydrogen’s rapid diffusion, which accelerates crack propagation along the grain boundaries.