Determination of the relative surface areas of PVD coatings by electrochemical impedance spectroscopy

The application of electrochemical methods for the determination of the real surface area of PVD coatings is explored. Titanium and chromium coatings with different growth morphologies and surface topographies were fabricated by magnetron sputtering. The morphology was characterized by SEM and its effect on the electrochemical polarization behavior of the coatings was studied by linear sweep voltammetry in 5 M HCl and 0.66 M NaCl. The nominal current densities measured were consistently higher for coatings having a coarse microstructure. Impedance spectroscopy was used to determine the real surface area of the films relative to a flat surface produced by mechanical polishing. When corrected for the real surface area, the polarization current density at a given potential did not depend on film morphology, both for titanium and chromium. The present paper demonstrates that electrochemical impedance spectroscopy is a useful method for the estimation of the surface area of PVD coatings.