Properties of stainless-steel surface after hollow cathode assisted plasma nitriding

AISI 304 stainless steel was nitrided at different temperature in the plasma equipment using a new auxiliary device. The proposed hollow cathode auxiliary device improves the plasma density, thereby accelerating the nitriding process. The modified surface was characterized by x-ray diffraction, scanning and transmission electron microscopies, atomic force microscopy, surface microhardness testing. Electrochemical corrosion test was used to measure the localized corrosion resistance of the samples. Single S-phase layer without the CrN precipitation was obtained by hollow cathode plasma nitriding at 450 degrees C, which improved the microhardness, wear and corrosion resistance of the steel surface. Nitriding at higher temperature of 550 degrees C resulted in substitution of the S-phase towards layer composed from CrN and alpha-Fe phases, improving the microhardness but decreasing the corrosion resistance.