The electrochemical behavior of thermally oxidized CrN coatings deposited on steel by cathodic arc plasma deposition

Cathodic arc plasma deposition of the CrN coating has been applied to an industrial scale to improve the corrosion resistance of the AISI 304 stainless steel. Thermal oxidation in air was carried out at the temperature of 500 and 800 8C for 1 h. The effect of the thermal oxidation on the aqueous corrosion behavior of the CrN/304s assembly was investigated in this study. The composition and structure of the CrN coatings were studied by the grazing X-ray diffraction (GXRD), electron probe X-ray microanalyzer (EPMA), and X-ray photoelectron spectroscopy (XPS). The polarization resistance (Rp) of all samples was measured and compared in terms of a polarization resistance resulting from electrochemical impedance spectroscopy (EIS) in a mixture of 0.5 M H2SO4 þ 1 M NaCl solution. The results indicated that the corrosion resistance of the CrN coated steel oxidized at 500 8C is significantly reduced. On the contrary, the electrochemical behavior of the CrN coated steel oxidized at 800 8C shows better corrosion resistance than the one oxidized at 500 8C and as-deposited steel. After thermal oxidation at 800 8C, the oxide layer formed on top of CrN coating enhances the corrosion protection of the CrN coated steel.