High-density plasma nitriding of AISI 316L for bipolar plate in proton exchange membrane fuel cell

After plasma nitriding, a nitrogen-expanded austenite layer, the so-called S-phase is formed in all nitrided samples. The ICR value of the nitrided samples decreases to approximately 10 mΩcm2 after plasma nitriding. The sample nitrided at 590 K shows the best corrosion property, while the corrosion resistance of the sample nitrided at higher temperatures decreases because of the formation of Cr-depleted regions in the nitrided sample. By using high-density plasma, the process temperature can be reduced to such a low temperature that Cr depletion is not significant, but a dense S-phase is formed.