Influence of plasma diffusion-based surface modifications on the corrosion behavior and the contact resistance of stainless steels

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The climate-neutral production of hydrogen and the use of hydrogen as an energy carrier in fuel cells represent the technologies of the future against climate change accelerated by fossil energy carriers. Austenitic rust- and acid-resistant (RS) steels in particular are gaining increasing attention in research and development with regard to alternatives materials for bipolar plates in polymer electrolyte membrane (PEM) electrolysis. Austenitic steels also offer enormous potential for saving volume and increasing efficiency compared to graphite-based bipolar plates and at the same time represent an economical alternative to expensive titanium or nickel based materials. Chromium dissolved in the austenitic steel causes the high corrosion resistance through the formation of a corrosion-resistant, insulating passive layer, which is determined by the combination of the individual alloing elements of the autenitic steels. However, this passive layer increases the interfacial contact resitance (ICR). The reduction of the ICR therefore requires suitable surface treatment of the austenitic steels. Empirical research shows a significant reduction in the electrical surface resistance for plasma nitrided austenitic steels compared to the untreated variants and show comparable or even better corrosion resistance. Therefore, it can be concluded that other mechanisms of corrosion protection apply to nitrided autenitic steels than are the case for the corrosion-protecting, electrically insulating passive layer on untreated steels.Since the plasma nitriding of austenitic steels, which has long been established, primarily aimed at improving the wear behavior while maintaining the positive corrosion properties, there are currently no mechanism-based findings or models that describe the physicochemical mechanisms regarding the conductivity of nitrided RS steels through the surface modification. This knowledge gap has to be closed by means of appropriate basic research in order to develop the enormous potential of plasma nitrided autenitic steels for use in hydrogen technology. The basic knowledge of the processes of surface layer constitution and electic properties down to the atomic level requires the combination of modern electrochemical and microstructural characterization methods with corresponding simulation models.This need for research is taken up in the proposed project by analyzing the influence of chemical, microstructural and atomic properties of the austenitic RS steels modified by plasma nitriding on the resulting electrical and electrochemical properties on the basis of material analysis and simulation methods and describing them in a mechanism-based manner.