Analytical–experimental approach for accurate depth profile evaluation of diffusion zone in plasma nitrided iron

Nitrogen depth profile of diffusion zone in plasma nitrided pure iron was analytically calculated and experimentally measured. Nitrogen concentration equation was obtained versus nitriding temperature, time and diffusion distance. Plasma nitriding was carried out on pure iron substrate at 550°C in an atmosphere of 75H₂–25N₂. Nitrogen concentration depth profile in compound layer was characterised by glow discharge optical emission spectroscopy (GDOES) and for detection of nitrogen within the diffusion zone, secondary ion mass spectroscopy (SIMS) technique was employed. Nitrogen diffusion depths were measured accurately by optical and scanning electron microscopy as well as SIMS technique at different nitriding times. Experimental results indicated good agreement with calculated diffusion depths for various nitriding cycles. The extent of nitrogen diffusion depth in alpha zone, detected in this work for 10 h plasma nitriding at 550°C, was in excess of 2000 μm; such values have not been reported in previous investigations that conventionally used EDS, GDS, XPS or EPMA technique.