Collision Dissociation Model in Ion Nitriding

Specimens of iron and various steels were ion nitrided in different atmospheres at different ionic energy levels. A collision dissociation model of ion nitriding is proposed, based on the results of ion nitriding tests and calculations of the densities of ions and neutral particles in the cathode potential drop region, incorporating analysis of the collision process and cathode sputtering effects. In ion nitriding there are several possible processes of nitrogen atom migration from gas phase to solid phase, but ion nitriding is achieved primarily by penetration of active nitrogen atoms produced by collision dissociation. The energy conditions of N2, NH3, and N2–H2 in collision dissociation were analysed and the amount of active nitrogen atoms was calculated semiquantitatively. The calculated values were in agreement with the results of the nitriding tests. The effects of H2 on collision dissociation and the heating of the cathode during ion nitriding are also discussed.