Corrosion resistance of tungsten carbide-rich coating layers produced by noble gas ion mixing

Abstract

Tungsten carbide (WC) belongs to the class of protective coatings due to its good mechanical properties and corrosion resistance. Herein WC-rich coating layers have been produced by irradiating C/W multilayers with noble gases at room temperature. The in-depth concentration distributions after ion irradiation have been measured by Auger electron spectroscopy depth profiling. The corrosion resistance of the formed layers has been tested in 3.5 wt% NaCl solution. It has been shown that the growth of the WC-rich layer started at the interfaces and with increasing fluence the separately growing layers coalesced. With the coalescence of the layers the corrosion resistance of the system suddenly increased. To describe this phenomenon the term effective areal density has been introduced. If the effective areal densities of WC were lower and higher than 550 (1/nm2) and 1200 (1/nm2), the corrosion current densities were 0.5 and 0.08 (µA/cm2), resp. The in-depth distribution of the WC-rich layer and thus the corrosion resistance could be tailored by varying the projectiles, fluences, energies and initial layer structure. The maximum corrosion resistance found was better than that of stainless steel and WC cermet. The effective areal densities could be predicted by TRIDYN simulations allowing the design of corrosion resistive coatings.