Resistance of nanoscale multilayer C/Cr coatings against environmental attack

Nanoscale multilayer C/Cr coatings were deposited on stainless steel substrates by the combined steered cathodic arc/unbalanced magnetron sputtering technique. The substrates were treated by Cr+ ion etching, followed by the deposition of a 0.25 μm thick CrN base layer and finally a C/Cr multilayer coating deposited between − 65 and − 350 V. This paper studies the influence of the bias voltage on the oxidation and corrosion performance of C/Cr coatings. The oxidation behaviour of C/Cr coatings was investigated using thermogravimetric analysis (TGA) through dynamic oxidation from room temperature to 1000 °C in air and isothermal heat-treatment at temperatures selected based on the TG traces. The corrosion performance of the films was studied by means of potentiodynamic polarisation test using a 0.01% NaCl solution. The surfaces of the samples after oxidation and corrosion testing were examined using Raman spectroscopy, XRD, and SEM/EDX. The results show that C/Cr coated substrates were protected by Cr2O3 up to at least 700 °C (depending on the substrate bias voltage), which suggests the potential use of C/Cr coating for high temperature applications.