Evaluation of the Diffusion Coefficient of N in γIron Nitride:Influence of the Nitriding Potential

摘要

This work deals with a study of the nitriding potential effect on development of thecompound layer during the gas nitriding of Armco Fe samples. The gas nitriding experiments wereperformed in an atmosphere of partially dissociated gas ammonia (NH3) at 520 °C under a nitridingpotential varying from 0.25 to 3.5 atm~(-0.5)during 2 h. Through this experimental work includingXRD analysis, optical and SEM observations of the cross-sections of the treated samples, it isshown that the microstructural nature of the compound layer depends upon the nitriding potentialvalue. By use of the inverse problem based on a diffusion model previously published, it waspossible to estimate the diffusion coefficient of N in'( iron nitride as a function of the appliednitriding potential. XRD analysis has shown that the compound layer was composed of γ' ironnitride. A linear semi-logarithmic relationship relating the nitriding potential to the diffusioncoefficient of nitrogen in y iron nitride was also derived.