GROWTH-KINETICS OF CONCOMITANT NITRIDE LAYERS IN POSTDISCHARGE CONDITIONS - MODELING AND EXPERIMENT

In this study we present our results of experiments and theoretical mo del calculations of post-discharge nitrided iron and carbon steel. The model considers growth of up to three compact concomitant nitride lay ers. The growth is described in terms of mass balance between phases i n thermodynamic equilibrium. The results of the model, in terms of lay er thicknesses, are compared with those experimentally obtained in nit riding post-discharge assisted process. In this case, the layer growth is not affected by sputtering phenomena of the surface as it would be for ion plasma nitriding. The model considers flat front growth of th e layers throughout the treatment. We have found that the solved equat ions are extremely sensitive to small variations in the values of the nitrogen diffusion coefficients being considered. For short treatment times, we have observed that the layer growth does not always obey a p arabolic profile, and that the flat front condition is not always met, which in turn could generate growth that surpasses the parabolic regi me.