Spatial distribution of active species during post-discharge nitriding

Abstract

The spatial distribution of active species during nitriding in a plasma post-discharge flow was investigated in a microstructural study linked with models to predict the atmospheric density of atomic nitrogen. Pure iron pieces were nitrided at 560°C for 10 min in an N2-H2-Ar mixture in the post-discharge flow of a microwave plasma reactor. The distribution of the species was experimentally evaluated in terms of the nitriding precipitation behaviour at different positions along the quartz tube of the reactor. The nitrided specimens were analysed by optical and scanning electron microscopy as well as X-ray diffraction. The treated pieces developed a microstructure with a nonuniform distribution of nitrides over the surface. These results indicate that there is a gradient in nitrogen potential along the length of the quartz tube of the post-discharge reactor and are consistent with the nitrogen atomic density distribution values estimated using the models.