On the corrosion behavior of multilayered WC–Ti1−xAlxN coatings on AISI D2 steel

In the present work, multilayered coatings with alternate layers of WC–Ti and WC–Ti1−xAlxN were deposited for use as wear-resistant and corrosion-resistant surfaces. Ti and TiN base layers were deposited on the substrate prior to the multilayers. WC–Ti1−xAlxN coatings with variable Al content (i.e., Al target power density) were deposited onto a steel substrate (high-speed steel; HSS) by the cathodic arc deposition method. The Al content could be controlled using an evaporation source for Al and fixing the evaporation rate of the other target sources. Four kinds of WC–Ti1−xAlxN coatings were prepared (WC–Ti0.6Al0.4N, WC–Ti0.53Al0.47N, WC–Ti0.5Al0.5N and WC–Ti0.43Al0.57N). The corrosion behavior of WC–Ti1−xAlxN 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 content on the coating properties related to the corrosion behavior. The galvanic corrosion current measured between the coating and substrate showed a low value. The results of potentiodynamic polarization tests indicated that the WC–Ti0.43Al0.57N coating with lower porosity enhanced the corrosion resistance. In electrochemical impedance spectroscopy measurements, the WC–Ti0.43Al0.57N coating showed two time constants and decreased the charge transfer resistance of the coating (Rct). Multilayered coatings were analyzed by EDS and XRD techniques to evaluate the crystal structure and compound formation behavior. Surface and cross-sectional morphology of the films was observed using SEM. In addition, scratch tests were performed to measure film adhesion strength.