Effect of Microstructure on the Mechanical Response of Hydrogen-Charged Pure Iron

In this paper, we investigate how two different microstructures in pure iron affect the dislocation mobility in hydrogen-charged and non-charged samples by conducting stress-relaxation tests. The effective activation volume of the pure iron for both types of microstructures (cold-rolled and annealed samples) has been determined for both H-charged and uncharged material. Information about the dislocation structures formed during stress relaxation is provided by conducting TEM analysis. We employ a self-consistent kinetic Monte-Carlo (SCkMC) model of the 1/2 [111] screw dislocation in Fe to investigate how hydrogen affects the mobility and behavior of the dominant mobile dislocation in Fe at different stresses and H concentrations. The results from our simulations show the following: (i) at low stresses the deviation from the primary slip plane in the presence of H is lower than the deviation in the uncharged Fe. The deviation angle decreases with increasing H concentration; (ii) at higher shear stresses, the higher probability for kink-pair formation in the secondary (110) planes in the presence of H, leads to an enhanced deviation from the primary slip plane, which increases with increasing H concentration. We use the results of stress-relaxation tests and SCkMC simulations to propose an explanation for the formation of dislocation cell structures in pure and hydrogen charged Fe in the cold-rolled and annealed samples.

Automated summary

In this study, the effect of two different microstructures in pure iron on the dislocation mobility in hydrogen-charged and non-charged samples was investigated. Stress-relaxation tests and TEM analysis were conducted to determine the activation volume and dislocation structures formed during stress relaxation. A self-consistent kinetic Monte-Carlo (SCkMC) model was used to investigate the mobility and behavior of the dominant mobile dislocation in Fe under different stresses and H concentrations. The results showed that the presence of H affected the deviation from the primary slip plane and the formation of kink-pairs in the secondary planes at different stress levels and H concentrations. An explanation for the formation of dislocation cell structures in pure and hydrogen-charged Fe in the cold-rolled and annealed samples was proposed based on the results of stress-relaxation tests and SCkMC simulations.