Surface modification and corrosion properties of implanted and DLC coated stainless steel by plasma based ion implantation and deposition

Abstract

The aim of this investigation was to find a suitable pretreatment for the subsequent deposition of DLC films on a steel substrate. The implantation should on the one hand improve the corrosion properties of the steel substrate and on the other hand increase the adhesion of the DLC film to the substrate. Three different gases (oxygen, nitrogen, ethylene) were used for the implantation (voltage pulses of -10 kV), and the deposition (-15 kV) was performed with C2H4 on stainless steel substrates and silicon wafer by plasma based ion implantation and deposition (PBII&D). The influence of the different implantation gases on the composition, structure and corrosion resistance of the surface was studied. The surface morphology was changed depending on the working gas. In all implantation samples a composition gradient layer in the surface was confirmed by measurement of the depth distribution by SIMS and XPS. The DLC films as prepared with C2H4 PBII&D exhibited roughness, hardness, and friction properties similar to those of DLC films prepared by other hydrocarbon gases. The corrosion protection potential in an aqueous environment was evaluated by cyclic voltammetry. The oxygen and nitrogen implantations improved the corrosion protection properties. These two pretreatments also exhibited a good corrosion protection in combination with the DLC film coatings. This is due to the resulting bonding states in the implanted surface and due to an increased adhesion of the DLC films to the substrates as could be seen after the corrosion tests