Investigation of the mechanism of the corrosion fatigue by analysis of cyclic strain and current response

Corrosion fatigue tests on a commercial iron were carried out in a borate buffer solution containing 5 mol/m³ NaCl to clarify the evolution mechanism of the damage current during cyclic straining. By analyzing the strain and current response induced by the triangular load waveform, it was found that the damage current steeply increased just after a threshold strain on the loading cycle and decayed after the maximum strain on the unloading cycle. In order to investigate the relationship between the deformation at the crack tip and the current response during decreasing strain, the current decay induced by the triangular strain was compared with that induced by the trapezoidal strain. It was found that the decay rate of the current induced by the triangular load waveform was faster than that induced by the trapezoidal load waveform. Therefore, this current response induced by the trapezoidal load waveform was simulated by assuming that this response was attributed to anodic dissolution and repassivation at the fresh surface emerged during the loading cycle. The simulated current was in good agreement with the current response measured in the experiment. Consequently, the damage current induced by the triangular load waveform can be attributed to the anodic dissolution and repassivation processes at the crack tip, fundamentally. However, it was found that this current is also influenced by the deformation at the crack tip during a decrease in the strain.