Application and development of electrochemical methods to investigate the permeability of PVD coatings

According to the literature and state of the research, the analysis of the permeability of a coating system can be reduced to just the evaluation of the interaction between the substrate and the electrolyte through the coating. The further development of electrochemical methods capable to deliver specific information about this interaction was the core of this investigation. To achieve this objective, the electrochemical ion detection was proposed and further developed. The idea was the use of the iron ions generated in the substrate, due to the anodic dissolution. By using an ion detector, the permeability of the coating was evaluated as a function of the amount of detected iron ions. The results of these measurements are currents. A higher current indicate more ions, hence higher open porosity. By comparing the different samples it is possible to determine the permeability as function of the measured currents. Two different approaches were used to evaluate the capabilities of the method. First the method was used in conjunction with SECM. In this way, the ion detection was carried out with local resolution. The viability of the method was tested by analysing several samples with different artificial defects. By using a macroelectrode as ion detector, the results are not obtained with local resolution. However, the entire surface of the sample was analysed. For this reason, the results represent the permeability of the entire coating. In addition, the measurements were done with and without polarization of the sample. According to the results, the proposed test method has several important advantages to investigate the permeability by studying specifically the interaction between the substrate and the electrolyte.