NUKLEONIKA 2004, 49(2):57-60

INTERACTION OF NITROGEN ATOMS IN EXPANDED AUSTENITE FORMED IN PURE IRON BY INTENSE NITROGEN PLASMA PULSES

Jerzy Piekoszewski1,2, Bożena Sartowska2, Lech Waliś2, Zbigniew Werner1,3, Michał Kopcewicz4, Friedrich Prokert5, Jacek Stanisławski1, Justyna Kalinowska4, Władysław Szymczyk1

1 The Andrzej Sołtan Institute for Nuclear Studies, 05-400 Otwock/Świerk, Poland
2 Institute of Nuclear Chemistry and Technology, 16 Dorodna Str., 03-195 Warsaw, Poland
3 Institute of Physical Chemistry PAS, 44/52 Kasprzaka Str., 01-224 Warsaw, Poland
4 Institute of Electronic Materials Technology, 133 Wólczyńska Str., 01-919 Warsaw, Poland
5 Forschungszentrum Rossendorf e.V., Institut für Ionenstrahlphysik und Materialforschung, Postfach 510119, D-01314 Dresden, Germany

The paper presents the results of experiments on modification of pure iron by high-intensity nitrogen pulsed-plasma treatment. The duration of nitrogen plasma pulses is approximately 1 ms, and the energy density amounts to about 5 J/cm2. Such pulses are capable to melt the surface layer of the substrate (1-2 mm) and to introduce a significant concentration of nitrogen into the molten layer. Nuclear reaction analysis (NRA), X-ray diffraction (XRD) and conversion electron Mössbauer spectroscopy (CEMS) were used for characterisation of the treated samples. The main results of the data analysis are as follows: it has been stated that such treatment leads to gradual transformation of initial a-phase into austenitic g structure in which expanded austenite gN is present. Treatment with 20 pulses results in almost complete transformation and introduces a retained dose of nitrogen estimated as 5.5 ´ 1017 N/cm2. The susceptibility for expansion of the lattice transformed to austenite in this way is smaller than in the case when the steel subjected to conventional nitriding is originally of austenite type.
The analysis of the ratio of g to gN as a function of the nitrogen content provides a firm evidence that strong repulsion forces act between the first and the second nearest-neighbour nitrogen atoms in the fcc austenitic structure formed as a result of nitriding of pure iron by intense nitrogen plasma pulses.