Effect of Al additions in WC-(Cr₁₋ₓAlₓ)N coatings on the corrosion resistance of coated AISI D2 steel in a deaerated 3.5 wt.% NaCl solution
By Lee, J.H.; Ahn, S.H. & Kim, J.G.
Published in Surface and Coatings Technology
2005
Abstract
Multilayered WC-(Cr₁₋ₓAlₓ)N coatings were deposited on AISI D2 steel using cathodic arc ion plating (CAIP) process. Five kinds of WC-(Cr₁₋ₓAlₓ)N coatings were prepared: WC-Cr₀.₆Al₀.₄N, WC-Cr₀.₅₇Al₀.₄₃N, WC-Cr₀.₅₃Al₀.₄₇N, WC-Cr₀.₄₈Al₀.₅₂N and WC-Cr₀.₄₅Al₀.₅₅N. The Al concentration could be controlled by using evaporation source for Al targets and fixing the evaporation rate of the other metals (WC alloy and Cr). In this study, the corrosion behavior in deaerated 3.5 wt.% NaCl solution was investigated by electrochemical corrosion tests (potentiodynamic polarization test, galvanic corrosion test, electrochemical impedance spectroscopy (EIS)) and surface analyses (glow discharge optical emission spectroscopy, X-ray diffractometry, scratch adhesion test, scanning electron microscopy, electron probe micro-analyzer). The results of potentiodynamic polarization test showed that the WC-Cr₀.₄₈Al₀.₅₂N coating with lower porosity exhibited the lower corrosion current density. The galvanic corrosion current between the coating and the substrate showed low values. In EIS measurements, the charge transfer resistance (Rct) value of WC-Cr₀.₄₈Al₀.₅₂N coating only increased with the immersion time, when compared to the other coatings. It can be due to the corrosion products plugging the pores and increasing the pathway resistance.