Investigation by fast video imaging of the micro-discharges occurring during the PEO process

This work aims at studying the micro-discharges (MDs) appearing consequently to the layer breakdown during the plasma electrolytic oxidation process. These MDs are not stationary and their evolution can be characterized by different time scales. In fact, depending on the variation in dielectric thickness, the electrical characteristics of the material surface change. This results in changes in the individual MD current density which affect also the discharge lifetime and distribution over the surface. The number, localization and aspect of the MDs evolve with time over the PEO treatment. Using fast video imaging allows us to determine the discharge lifetime and distribution over the sample surface. MDs do not appear over the whole current pulse since they are driven by the variation of the resulting voltage. By increasing the imaging frequency we determine that the MDs lifetime usually does not exceed 10 $\mu $s and that it ``blinks'' rapidly at the same location over the current pulse duration.