A numerical model for current transients during micro-indentation of passive iron surface

During in situ micro-indentation of passive iron in pH 8.4 borate solution, a couple of anodic current peaks emerged; the first peak during loading and the second peak during unloading. The current transients, associated with rupture and repair of the passive film, were influenced by the indentation conditions. For instance, the current peak height, the current peak area and the time required for complete repassivation are strongly dependent on indentation rate. A numerical model was proposed to correlate the current transient during loading with mechanical deformation of the passive surface. The comparison between the current transient measured experimentally and that estimated from the load transient suggested that the ruptured area of passive film was about 10% of the surface area deformed by the contact with the indenter.