For many industrial applications, the phenomena of high temperature oxidation and hot corrosion limit the applicability of engineering alloys. High temperature oxidation and corrosion result in a time-dependent loss of load-carrying wall-thickness, and hence a limited service life. High working temperature, requires the application of high Cr austenitic stainless steels or even Ni-based alloys, which are more expensive than the conventional low-Cr steels.
Alternatively, the possibility of creating a corrosion-protection layer system composed of Fe, Ni and Cr on a plain carbon steel substrate by means of electroplating is investigated within this study. Additionally, the stainless-steel-like properties of the generated system after appropriate heat treatment are examined. It is shown that interdiffusion takes place between the individual layers, which transform these into a gradient structure. Furthermore, heat treatment of the layered coating system produces dense homogeneous diffusion coatings. Numerous stainless-steel-like compositions can be formed using the layering process. Therefore, customization of a synthetic stainless steel is possible. Electrodeposition has been recognized as an attractive approach for the preparation of materials, either as coating or as freestanding object even in complex shapes. The proposed layer-by-layer electrodeposition process is followed by diffusion annealing, where interdiffusion of the various elements cause a redistribution of the phase composition, leading to a gradient corrosion-resistant layer.
Three different layer-systems were manufactured. Two specimen are single-layer-systems, where the low-carbon steel (RS275) has been covered by a Cr-layer (Cr/RS275), and Ni-layer (Ni/RS275), respectively. The third sample is a two-layer-system Cr/Ni/RS275 with Ni-layer on RS275-subtrate capped by Cr.
In order to quantify the interdiffusion behavior, all specimen were cut, ground and polished. Microstructural characterization was carried out by means of scanning electron microscopy (SEM) in combination with energy-dispersive X-ray spectroscopy (EDX). First simulations of the observed interdiffusion process were realized by the cellular automata approach which has been successfully applied to internal corrosion processes.