NITRIDE NANOPHASES IN A PLASMA-ASSISTED SURFACE-MODIFIED STEEL

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).