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作为燃料电池的能源载体的使用代表了未来应对气候变化的技术，化石能源载体加速了气候变化。特别是奥氏体防锈和耐酸（RS）钢在聚合物电解质膜（PEM）电解双极板替代材料的研究和开发中越来越受到关注。与石墨基双极板相比，奥氏体钢在节省体积和提高效率方面也具有巨大的潜力，同时也是昂贵的钛或镍基材料的经济替代品。铬溶解在奥氏体钢中，通过形成一个耐腐蚀的绝缘钝化层，使其具有很高的耐腐蚀性，这是由奥氏体钢的各个允许元素的组合决定的。然而，这种无源层增加了界面接触电阻（ICR）。因此，降低ICR要求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电表面电阻显着降低，并且显示出相当甚至更好的耐腐蚀性。因此，可以得出结论，其他的腐蚀防护机制适用于氮化奥氏体钢，而不是未经处理的钢上的防腐、电绝缘钝化层。由于奥氏体钢等离子体氮化的主要目的是改善磨损性能，同时保持良好的腐蚀性能，目前还没有基于机制的发现或模型来描述通过表面改性提高氮化RS钢电导率的物理化学机制。为了开发用于氢技术的等离子体氮化奥氏体钢的巨大潜力，必须通过适当的基础研究来弥补这一知识差距。对表面层构成和电学性质的基本认识，需要将现代电化学和微结构表征方法与相应的仿真模型相结合。在材料分析和模拟方法的基础上，通过分析等离子体氮化改性奥氏体RS钢的化学、显微组织和原子性能对电学和电化学性能的影响，并以基于机理的方式描述它们，提出了这一研究需求。

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.