Corrosion behavior of (Ti-Al-Cr-Si-V)xNy coatings on mild steels derived from RF magnetron sputtering

Multi-component metallic (MC) and multi-component nitride (MCN) coatings was deposited on mild steel substrates with the multi-component Ti-Al-Cr-Si-V target by adjusting nitrogen inlet in the sputtering process. Thickness of the coating was controlled around 1.7 mu m. Corrosion resistance of the MC and MCN coatings was investigated by Tafel plot and potentiodynamic polarization tests in 3.5% NaCl electrolyte. Although MCN coating exhibited favorable hardness, the corrosion current of the MCN 3 coating (i(corr)=19.4 mu A/cm(2)) was higher than that of mild steel (i(corr) = 16.4 mu A/cm(2)), indicating poor corrosion resistance and a porous structure derived from sputtering process. From the cross-sectional observation, numerous pinholes were found along the nano-columns in the MCN 3 coating. After introduction of 100 nm MC interlayer, these defects were suppressed and the calculated porosity rate was significantly decreased. The improvements on corrosion potential (E-corr =-520 mV) and current (i(corr) = 8.05 mu A/cm(2)) suggested that the MC/MCN coatings provided not only mechanical strength but also satisfactory anti-corrosion properties. (c) 2008 Elsevier B.V. All rights reserved.