Corrosion behavior of PVD-grown WC-(Ti1-xAlx)N films in a 3.5% NaCl solution

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-Ti(0.72)A(0.28)N 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. (C) 2002 Elsevier Science B.V. All rights reserved.