Abstract
Using cathodic arc plasma to deposit CrN on the steel has been explored and extensively studied to improve the wear and corrosion resistance of the steel structures. The extended research for the electrochemical behavior of CrN coated steel in aggressive solutions were investigated, and can be divided into two categories: The effects of “Metal vapor vacuum arc (MEVVA) implanted Cr interlayer” and “ thermal oxidation of CrN coatings “ on the electrochemical behavior of CrN coated steel . In the field of the interlayer function for the CrN coated steel, MEVVA source implantation is a novel and profitable surface modification process coupled with the cathodic arc plasma. The effect of the Cr implanted by MEVVA (Cr/steel) on the corrosion behavior of CrN/steel through the surface modification has been investigated. Both AISI 4140 steel and its coated assemblies of Cr/steel, CrN/steel, and CrN/Cr/steel were evaluated in an aerated 0.1N HCl solution. The composition and structure of the MEVVA implanted chromium and the cathodic arc plasma deposited CrN on steel were examined by XRD and TEM. The polarization resistance (Rp) of all samples was measured and compared with the results obtained from electrochemical impedance spectroscopy (EIS) simulated by an equivalent circuit to interpret the effect of MEVVA implanted chromium on the corrosion mechanism of the CrN/Cr/steel. The results indicated that the corrosion resistance of the CrN coated steel was significantly enhanced by the MEVVA implanted chromium in the CrN/Cr/steel assembly. In the field of thermal oxidation of CrN coatings, thermal oxidation in air was carried out at the temperature of 500oC and 800oC for 1 hour. The effect of the thermal oxidation on the aqueous corrosion behavior of the CrN coated AISI 304 steel assembly was investigated in this study. The corrosion resistance of all samples was compared in terms of a polarization resistance resulting from EIS in a mixture of 0.5M H2SO4 + 1M NaCl solution. The results indicated that the corrosion resistance of the CrN/304s oxidized at 500oC is significantly reduced. On the contrary, the electrochemical behavior of the CrN/304s oxidized at 800oC shows better corrosion resistance than the one oxidized at 500oC and as-deposited steel. After thermal oxidation at 800oC, the oxide layer formed on top of CrN coating enhances the corrosion protection of the CrN coated steel.