Corrosion behaviour of electrodeposited and sputtered Cr coatings and sputtered Ta coatings with α and β phases

The corrosion behaviour of α- and β-Ta coatings was compared to that of Cr coatings produced by cylindrical magnetron sputtering as well as electrodeposition. For Ta coatings, the corrosion process was dominated by dissolution of the steel substrate through open pores, however, at the end of 5 days, coating degradation was not observed. In contrast, while open pores were not observed with the Cr coatings, the corrosion resistance decreased as a function of time under acidic conditions, as a result of the protective oxide dissolution. Initially, however, the sputtered Cr coating exhibited improved corrosion resistance over the electrodeposited one, potentially due to the surface structure of the oxide film. Both Cr coatings showed similar transpassive behaviour to that of pure Cr; the current density of the sputtered Cr coating was observed to be greater than that of the electrodeposited one in the transpassive region due to the extensive droplet-like defects.