Characterization of iron nitrides prepared by spark erosion, plasma nitriding, and plasma immersion ion implantation

The effect of the nitrogen uptake in α-iron upon spark erosion in gaseous and liquid ammonia, plasma nitriding, and plasma immersion ion implantation is studied. The resulting phases and hyperfine parameters, measured by the Mossbauer spectroscopy, are discussed from the point of view of initial conditions of their preparation and subsequent heat and/or mechanical treatment. Spark erosion in the ammonia gas produces fine particles with the dominating ferromagnetic α-Fe phase (50%). The 20% of specimen volume form α′-Fe and α′′-Fe16N2 phases. The last 30% occupy the γ′-Fe4N, ferro- and paramagnetic e phases, and γ-Fe(N). Nitriding in the liquid ammonia allows to incorporate the higher content of nitrogen into α-iron particles which results in the formation of paramagnetic e(ζ)-Fe2N phase. This phase also dominates the surface of α-iron specimen implanted by nitrogen using plasma immersion ion implantation at 300°C/3 h, where high uptake of nitrogen (approx. 30 at%) is reached. Plasma nitriding at 510°C results in the formation of γ′-Fe4N phase.