A discharge of nitrogen - hydrogen mixture by 50 Hz pulsed dc in the presence of active screen cage is investigated by optical emission spectroscopy (OES). The aim is to identify the parameters (mixture ratio, filling pressure and current density) that may lead to high concentration of active species (N2, N2+ and N). The maximum concentration in this experiment is found with 40% H2 - 60% N2, at filling pressure of 3 mbar with current density of 5 mAcm-2. High carbon steel samples are nitrided for 1 - 4 hours at 500ºC and the treated samples are characterized by X - ray diffraction (XRD), Raman spectroscopy and Vicker's micro - hardness testing. The XRD spectra show different phases of nitrides (Fe2 - 3N, FeN, CrN) along with iron oxides. The Raman spectra confirm the formation of α - β (C3N4). The surface hardness is found to increase up to six times for 2 hour treatment.
Cathodic cage; plasma nitriding; edge effect
