A study on the quantitative determination of through-coating porosity in PVD-grown coatings

The corrosion resistance of coatings produced by PVD method was mainly based on two factors: (i) the degree of porosity in the coatings; (ii) the interdiffusion and adhesion of the coating-substrate system. The presence of porosity in the coatings can rapidly lead to the electrochemical dissolution of the substrate. The characterization of porosity in the coatings is indeed for quality assurance and coating process optimization. Thus, the characterization of porosity in a quantitative manner is of great interest to researchers. Recent technological advances in porosity measurement using electrochemical methods have resulted in overcoming the traditional porosity measurement limitations. The trends of porosity as a function of immersion time were evaluated by electrochemical impedance spectroscopy (EIS) measurement. Also, it was found that the accurate porosity measurement depended strongly on the correlation between the porosity enlarged ratio and the charge transfer resistance, which defined the critical time. (C) 2004 Elsevier B.V. All rights reserved.