A study of the mechanisms of ion nitriding by the application of a magnetic field

A model for ion nitriding is proposed which is based on the formation and diffusion of vacancy-nitrogen ion pairs. A theoretical expression is developed for the local effective diffusion coefficient of the combined vacancy-ion pairs which explains the accelerated case hardening associated with ion nitriding as compared with conventional nitriding. Ion-nitriding experiments on AISI 304 stainless steel were performed in a magnetic field to increase the number of vacancy-ion pairs. The experiments confirmed the theory, showing that in the current density range 100 -1000 A m^-2 the local effective diffusion coefficient is proportional to the current density.