Strip hollow cathode method for plasma thermochemical treatment for surface modification of thin metal strips: Plasma nitriding of austenitic stainless steel sheets for bipolar plates

• Strip hollow cathode method for plasma thermochemical treatment has been developed.
• Significantly decreased interfacial contact resistance of EN 1.4301 stainless steel.
• Improved anticorrosion properties of EN 1.4301 stainless steel.
• The method is very promising for continuous plasma nitriding of metal strips.

Beside its conventional applications such as improving the wear resistance of machine parts and tools, plasma thermochemical treatment (PTT) can be successfully used as a method for surface modification to achieve specific surface properties. Surface electrical conductivity of austenitic stainless steel sheets, for example, can be significantly enhanced by means of plasma nitriding. Such materials are of interest for the use as bipolar plates of proton exchange membrane fuel cells (PEMFC). In this regard a new PTT method based on a strip hollow cathode (SHC-PTT) has been developed as a cost-effective process for surface modification of thin metal strips in continuous operation. A laboratory-scale SHC-PTT device operating in stationary treatment mode has been realized and short-time plasma nitriding of EN 1.4301 (AISI 304) austenitic stainless steel sheets has been studied. The obtained nitrided layers were investigated using GDOES and XRD. Further, the interfacial contact resistance of the sheets was measured and the corrosion behaviour was investigated by means of electrochemical methods. The obtained results clearly demonstrate the high potential of the new SHC-PTT method for further development in terms of treating thin steel strips in continuous operation.