Growth kinetics of concomitant nitride layers in post-discharge conditions: modeling and experiment

Abstract

In this study we present our results of experiments and theoretical model calculations of post-discharge nitrided iron and carbon steel. The model considers growth of up to three compact concomitant nitride layers. The growth is described in terms of mass balance between phases in thermodynamic equilibrium. The results of the model, in terms of layer thicknesses, are compared with those experimentally obtained in nitriding 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 the layers throughout the treatment. We have found that the solved equations 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 parabolic profile, and that the flat front condition is not always met, which in turn could generate growth that surpasses the parabolic regime.