High-efficient surface modification of thin austenitic stainless steel sheets applying short-time plasma nitriding by means of strip hollow cathode method for plasma thermochemical treatment

• Strip hollow cathode method for plasma thermochemical treatment.
• High-efficient surface modification of thin austenitic stainless steel strip.
• Non-isothermal plasma nitriding at a strip velocity of 23 m h−1 appears feasible.
• Improvement of the electrical contact conductivity and corrosion resistance.
• Excellent surface properties regarding metallic bipolar plates for PEM fuel cells.

The present work is devoted to the short-time plasma nitriding of EN 1.4301 (AISI 304) austenitic stainless steel sheets in a pulsed glow discharge by means of a novel strip hollow cathode process for plasma thermochemical treatment (SHC-PTT) aiming at their use as bipolar plates of proton exchange membrane fuel cells (PEMFC). The fundamental trends in the change of the interfacial contact resistance (ICR) and corrosion resistance in dependence on the duration of plasma nitriding were studied. The investigations were focused on the capability of the method to reduce the ICR without deterioration of the corrosion resistance in a high-rate process. Within the range of experiments it could be shown that at a certain temperature, defined by improved or at least non-deteriorated corrosion resistance, the plasma nitriding rate is determined by the requested value of ICR. The simultaneously reduced ICR and improved corrosion resistance are explained by the formation of chromium nitrides on the substrate surfaces during the plasma nitriding. Acceptable ICR and corrosion resistance could be achieved in a continuous non-isothermal plasma nitriding process at a simulated strip rate up to 23 m h−1 with further potential to speed up the process.