Evaluation of Nitrogen Diffusion in Plasma Nitrided Iron by Various Characterization Techniques

Diffusion of nitrogen in plasma nitrided iron and structural evolution during the nitriding process were evaluated by several characterization techniques including optical microscopy (OM), microhardness depth profiling (HDP), scanning electron microscopy (SEM), x-ray diffraction (XRD), glow discharge optical emission spectroscopy (GDOES), and secondary ion mass spectroscopy (SIMS). Plasma nitriding was carried out on high purity iron substrate at a temperature of 550oC in an atmosphere of 75%H2-25%N2. Case depth, thickness of the compound layer, micro-hardness profile, nitrogen depth profile, and characteristics of intermediate nitrides including epsilon, gamma prime, and Fe16N2 were studied. The results of characterization of plasma nitrided iron indicated a good agreement with experimental findings; thus, the techniques confirmed one another. For accurate measurement of nitrogen within the diffusion zone, where concentration was below 0.1wt%, secondary ion mass spectroscopy technique was used. The extent of nitrogen diffusion detected by secondary ion mass spectroscopy in this work was greater than 1800 μm; a value which is not reported in the iterature.