In this work we present a study of the near surface phases present in
a 1018 steel nitrided by a weakly excited plasma in an ionic nitriding
reactor. Characterization of the plasma by optical emission spectrosc
opy identified N-2 and N-2(+) as the active species. From these data,
the vibrational temperatures were estimated assuming a Boltzmann distr
ibution for the vibrational levels. The microstructure of the nitride
layers was analyzed by transmission electron microscopy, scanning elec
tron microscopy and high resolution electron microscopy (HREM). Electr
on microscopy identified the equilibrium between the epsilon-Fe-2-5(C,
N) and gamma'-Fe-4(C, N) phases and HREM indicated that (0001)(epsilo
n)parallel to(111)(gamma). We have also identified the metastable alph
a ''-Fe-16(N, C)(2) phase in the alpha-Fe diffusion zone with the foll
owing relationship orientation: (020)(alpha '')parallel to(020)(alpha-
Fe) and [100](alpha '')parallel to[100](alpha-Fe).