INFORMATION DEPTHS OF CONVERSION X-RAY MOSSBAUER-SPECTRA IN PLASMA NITROCARBURIZED SURFACE-LAYERS

The depth sensitivity provided by the different penetration ranges of conversion electron and conversion X-ray Mossbauer spectroscopy (CEMS and CXMS) is used to distinguish the information obtained from the compound and diffusion layers at the surface of plasma nitrocarburized pure iron. CEMS, for its part, shows that the 12 mum compound layer consists mainly of the epsilon-phase (nitride/carbonitride) and theta-cementite in addition to a very small amount of alpha-ferrite, while the diffusion layer consists of ferrite. The results of X-ray diffraction are in good agreement with the Mossbauer results. CXMS, on the other hand, shows a contribution of ferrite to the total area under the Mossbauer spectrum of about 26%. This means that the depth of origin of the CXMS information must be greater than the thickness of the compound layer. This being unexpected, a new estimation of the information depth is attempted. The maximum depth of origin of the CXMS information for the magnetically split spectra is found to be about 30 to 50 mum.