Corrosion behavior of PVD-grown WC–(Ti₁−ₓAlₓ)N films in a 3.5% NaCl solution
By Balani, K.; Laha, T.; Agarwal, A.; Karthikeyan, J. & Munroe, N.
Published in Surface and Coatings Technology
2003
Abstract
WC–(Ti₁−ₓAlₓ)N coatings of stepwise changing Al concentration (WC–Ti₀.₈₆Al₀.₁₄N, WC–Ti₀.₇₂Al₀.₂₈N, and WC–Ti₀.₅₈Al₀.₄₂N) were deposited on AISI 1045 substrate by high-ionization sputtered PVD method. The Al concentration could be controlled by using evaporation source for Al and fixing the evaporation rate of the metals (WC alloy and Ti). The corrosion behavior of WC–(Ti₁−ₓAlₓ)N coatings in deaerated 3.5% NaCl solution was investigated by electrochemical corrosion tests and surface analyses. Particular attention was paid to the effects of Al target power density on the film properties related to the corrosion behavior. The measured galvanic corrosion currents between coating and substrate indicated that WC–Ti0.72Al0.28N coating showed the best resistance of the coating tested. The results of potentiodynamic polarization tests showed that this coating had passivation and lower porosity. This indicated that this coating is effective in improving corrosion resistance. In electrochemical impedance spectroscopy, the WC–Ti₀.₇₂Al₀.₂₈N coating showed one time constant loop and the increased polarization resistance of coating relative to other samples. The better corrosion performance of WC–Ti₀.₇₂Al₀.₂₈N coating is due to the modified compactness, porosity and adhesion of the coating layer.