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

The effect of the nitrogen uptake in alpha -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 alpha -Fe phase (50%). The 20% of specimen volume form alpha ' -Fe and alpha " -Fe(16)N(2) phases. The last 30% occupy the gamma ' -Fe(4)N, ferro- and paramagnetic epsilon phases, and gamma -Fe(N). Nitriding in the liquid ammonia allows to incorporate the higher content of nitrogen into alpha -iron particles which results in the formation of paramagnetic epsilon(zeta)-Fe(2)N phase. This phase also dominates the surface of alpha -iron specimen implanted by nitrogen using plasma immersion ion implantation at 300 degreesC/3 h, where high uptake of nitrogen (approx. 30 at %) is reached. Plasma nitriding at 510 degreesC results in the formation of gamma ' -Fe(4)N phase. (C) 2001 Elsevier Science B.V. All rights reserved.