Enhancement of the corrosion protection performance of Ni coatings on steel substrates using HiPIMS pretreatment

This paper adresses with the enhancement of corrosion resistance of steel substrates using High Power Impulse Magnetron Sputtering (HiPIMS) pretreatment before deposition of Nickel (Ni) coating by sputtering. Electrochemical measurements show that Ni exhibits a higher corrosion potential than steel. In this situation, slight imperfections in the Ni coating can cause severe anodic dissolution of the steel substrate in a corrosive environment. It is therefore necessary to optimize the steel surface preparation before depositing the Ni coating, as growth defects originate mainly from irregularities on the substrate surface (dust, polishing residues, impurities). In this work, we developed a HiPIMS pretreatment of the steel substrate. This latter is subjected to intense and homogeneous Ni ion bombardment using a Ni-Ar HiPIMS discharge and biasing the substrate at -600 V. We obtained an ultra-clean substrate surface and the formation of a Ni 1-x Fe x intermixed interface. Advantageously, the resulting modified surface provides an ideal template for the Ni layer to grow without open paths down to the substrate surface, resulting in corrosion resistance of the Ni-steel system for more than 1000 h in a salt spray bath, at room temperature.