Formas de representación del transporte de nitrógeno atómico en el sistema Fe-N: Estudio del estado estacionario en un proceso de nitruración post-descarga

Abstract

A moving boundary diffusion model for post-discharge nitriding is presented. This model assumes that the nitriding process does not depend on the parallel directions to the specimen surface, but only on the correspondent orthogonal direction. For a specimen of finite depth, different boundary conditions on its base are attached. Then, existence and uniqueness of the steady states of the considered models are studied. The examination of possible steady states under the assumption of certain qualitative behavior of the diffusion coefficients leads to analytic expressions for the nitrogen concentration profiles. The obtained analytic expressions, together with nitrogen concentration measurements at each phase and additional measurement of the nitrogen flux, allows to determine the diffusion coefficients as functions of the nitrogen concentration. It is therefore the object of the present work to provide a theoretically grounded method for obtaining analytic expressions of nitrogen concentration profiles and concentration-dependent diffusion coefficients. This method only uses measurements of the nitrogen concentration and the nitrogen fluxes and does not assume any ``a priori'' behavior of the layer growth.