Modelling post-discharge nitriding and nitrocarburising

Abstract
In this paper, the state of the art in the modelling of nitriding and nitrocarburising using late post-discharge processes is described. In a first part, interstitial diffusion in ternary system is treated. The problem of the diffusion in two-phase domains is evoked. The chemical pathways in N₂-H₂ and N₂-CH₄ post-discharges creating active species are next presented to try to identify the precursors responsible for the transport of nitrogen and carbon to the surface of the solid. Finally, attention is paid to the coupling between the gas phase and the solid. Two different approaches are proposed, either by considering a steady state or a transient gas flow. The latter requires to introduce a sequence of surface phenomena (adsorption, surface diffusion, recombination, dissolution...) that provides a rigorous way to couple processes in the gas phase and in the solid.