Effects of intermediate surface treatments on corrosion resistance of cathodic arc PVD hard coatings

Aiming to improve corrosion resistance of CrN coated tool steel parts, intermediate treatments were introduced to remove surface droplets and inclusions of cathodic arc CrN coatings midway of the deposition. Three intermediate treatments were examined: micro-blasting with two types of blasting media and Ar ion plasma etching followed by Ti ion bombardment. CrN coatings with two-layer structures were deposited on refined AISI D2 tool steel substrates. At the interface between the lower and upper layers of the coating, intermediate treatments were applied. Corrosion behavior of the coatings was studied by immersion tests and anodic polarization measurements in 10% sulfuric acid aqueous solutions. Observation of the coatings and their cross-sections was made using field emission scanning electron microscope with refection electron imaging, and focused ion beam scanning electron microscope. The results of the immersion tests showed that applying intermediate treatments enhanced the corrosion resistance of CrN coatings. Particularly, intermediate removal of the droplets and inclusions of a coating surface and smoothing the interface prevented formation of penetrated pathways throughout growth defects, thus preventing the formation of corrosion cells and improving the corrosion resistance of the substrate-coating system. Based on the findings of this study, intermediate treating of cathodic arc coatings showed a promising solution to improve corrosion resistance of coated parts operating at corrosive environments.