Compositional depth profile investigation of plasma nitriding by multiple analyses techniques

Compositional depth profile in plasma nitriding is investigated by several experimental techniques including EDS, GDOES and SIMS as well as a calculated method. Plasma nitriding was carried out on high purity iron substrate at a temperature of 550 °C in an atmosphere of 75 vol.% H2–25 vol.% N2 for time periods of 1, 2, 5 and 10 h. SEM and XRD methods were used for microstructural evaluation and phase identification. According to EDS, GDOES and calculated data, composition of the compound layer reached nearly to Fe-8 wt% N and Fe-6 wt% N indicating ε-Fe2–3N and γ′-Fe4N nitrides were formed, respectively. Although nitrogen concentration was decreased to nearly zero close to the nitrided surface, calculated data and SIMS profiles show very smooth gradient in diffusion zone down to several hundreds of micrometers. The results of compositional depth profiling by EDS, GDOES and SIMS indicated good agreement between experimental findings and, thus, the techniques completed one another. It was found that EDS and GDOES are appropriate for analysis of Fe and N in the compound layer, but both have limitations for profiling of nitrogen in the diffusion zone. SIMS, on the other hand, was distinguished as a professional technique for accurate measurement of nitrogen within the diffusion zone. The experimental depth profiles indicated good consistency with calculated diffusion profiles for all treatment cycles.

► Concentration depth profile in PN investigated by EDS, GDOES and SIMS techniques.
► Compound layer reached to Fe-8 wt% N and Fe-6 wt% N indicating ε-Fe2–3N and γ′-Fe4N.
► N decreased rapidly close to the surface with very smooth gradient in diffusion zone.
► EDS and GDOES were found suitable for analysis of Fe and N atoms in compound layer.
► SIMS, a high precision method, was successful for profiling of N in diffusion zone.