The corrosion behavior of Cr-(C,N) PVD hard coatings deposited on various substrates

A comparison was made between the electrochemical corrosion behavior of chromium carbonitride (Cr-(C,N)) and chromium nitride (Cr-N) coatings produced by evaporation in a thermionic-arc ion-plating apparatus at 450degreesC. These coatings were deposited on substrates in the form of discs of mild-steel (CK 45) and stainless-steel (SS 304). Potentiodynamic polarization tests, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) were the techniques used to, characterize the corrosion behavior. The potentiodynamic tests revealed the current density versus potential for the coated and uncoated substrates and the difference in their corrosion potentials (E-corr). In all cases the E-corr shifted to a more positive potential after the coatings were applied. The electrochemical impedance spectroscopy measurements as a function of immersion time were carried out in a 0.5 M NaCl solution at the E-corr. The corrosion properties, lower current density, and higher polarization resistance were found to be two to six times better than the uncoated substrate for the Cr-(C,N) coatings and two orders of magnitude better for the Cr-N coatings. (C) 2003 Elsevier Ltd. All rights reserved.