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

氢的气候中性生产和氢在燃料电池中作为能量载体的使用代表了未来应对化石能源载体加速的气候变化的技术。特别是奥氏体防锈和耐酸（RS）钢在聚合物电解质膜（PEM）电解中关于双极板的替代材料的研究和开发中获得越来越多的关注。与石墨基双极板相比，奥氏体钢还提供了节省体积和提高效率的巨大潜力，同时代表了昂贵的钛或镍基材料的经济替代品。溶解在奥氏体钢中的铬通过形成耐腐蚀的绝缘钝化层而导致高耐腐蚀性，这是由奥氏体钢的单个合金元素的组合决定的。然而，该钝化层增加了界面接触电阻（ICR）。因此，降低ICR需要对奥氏体钢进行适当的表面处理。经验研究表明，与未经处理的变体相比，等离子体氮化奥氏体钢的表面电阻显著降低，并且显示出相当或甚至更好的耐腐蚀性。因此，可以得出结论，与未处理钢上的腐蚀保护、电绝缘钝化层相比，其他腐蚀保护机制适用于氮化奥氏体钢。由于奥氏体钢的等离子体氮化已经建立很久，主要目的是改善磨损行为，同时保持积极的腐蚀性能，目前还没有基于机理的发现或模型来描述关于通过表面改性的氮化RS钢的导电性的物理化学机理。这一知识差距必须通过适当的基础研究来弥补，以开发等离子体氮化奥氏体钢在氢技术中的巨大潜力。表面层构成和电性能过程的基本知识需要将现代电化学和微观结构表征方法与相应的模拟模型相结合。通过分析化学，在材料分析的基础上，研究了等离子渗氮对奥氏体RS钢的微观结构和原子性能的影响和模拟方法，并以基于机制的方式描述它们。

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.