EFFECTS OF HYDROGEN ON IRON NITRIDING IN A PULSED PLASMA

A low frequency DC pulsed plasma used for iron nitriding is studied by means of an electrostatic probe and optical emission spectroscopy. The evolution of the electron density leads to the determination of the electron-ion recombination coefficient. The variations of this coefficient and the measurement of some emission lines of neutral iron and of excited states of neutral and ionic molecular nitrogen as a function of the percentage of H2 give additional insights into the role of hydrogen during the nitriding process. Thus the presence of vibrational states of nitrogen-N2(C3-PI-u, B3-PI-g, A3-SIGMA-u+), N2+(B2-SIGMA-u+)-late in the afterglow confirms their importance in such plasma assisted surface treatments.