Enhancement of diffusive oxidation resistance and topographical corrosion resistance of hot work tool steels by nickel multifunctional coatings

This research focuses on the positive effects that a metallic coating made with Nickel coating can have on the oxidation and corrosion behaviour of hot work tool steels (HWT). Two different types of hot work tool steels, each with a distinct amount of chromium, were analysed by means of the gravimetric oxidative method and corrosion testing. Using PVD deposition techniques, Nickel coating is deposited onto the steel specimens in order to achieve tailor made properties. Investigations into the diffusive oxidation behaviour of HWT steels are carried out at temperatures of 600, 700, and 800 C-degrees. Before and after going through the oxidation process, the surface morphologies of steel specimens are analysed using SEM and XRD instruments respectively. The initial stages of oxidation are characterized by rapid oxidation; however, as the time spent oxidising the specimens increases, the rate of oxidation slows down. As the temperature rises, the quantity of oxidation that may be tolerated drops. The ability of a specimen to resist oxidation is enhanced when it has a comprehensive uniform nickel coating. It is interesting to note that the oxidation resistance of both type HWT specimens coated by Nickel coating has increased by a factor of two. Intriguingly similar trend with three-fold increase in corrosion resistance of the aforementioned steels is achieved in red sea water when coated with Nickel.