Activation volume and density of mobile dislocations in hydrogen-charged iron

In order to monitor the influence of hydrogen on the coupled evolution of dislocation velocity and mobile dislocation density, we applied repeated transients to pure iron under simultaneous hydrogen cathodic charging conditions. The effective activation volume and the thermal stress were determined at different hydrogen concentrations. The effective activation volume decreases immediately with cathodic charging. At high hydrogen concentrations, the activation volume decreases and the thermal stress increases rapidly. The density of mobile dislocations in the hydrogen-charged iron has a lower rate of exhaustion than the hydrogen-free one. The thermal activation energy decreases and the average dislocation velocity increases as a function of hydrogen concentration. Transmission electron microscopy reveals hydrogen-induced tangled dislocations, which indicates a weakening of the repulsive stress field between dislocations.