Depth resolved and elemental selective XRF and XAS in surface layer of annealed Fe-Cr alloys

Cr in Fe-Cr alloys often forms some different phase of oxides during annealing at high temperatures. The phases of Cr oxides are determined depending on the annealing condition such as temperature and oxygen partial pressure. In this study, depth-resolved X-ray fluorescence analysis (XRF) of Fe and Cr were carried out using a two-dimensional pixel array detector with geometrical arrangement of the grazing exit in detection of fluorescence X-ray emitted from the sample surface, in order to characterize the depth-directional distribution of the elements in the surface layers of Fe-Cr alloys annealed under low oxygen partial pressure. In addition, depth-resolved X-ray absorption spectra will also be able to be obtained by measuring the incident X-ray energetic dependencies of the fluorescence intensity. These techniques facilitate non-destructive measurement of the elemental distribution and the phase of metal or oxides in depth direction. The experiments were performed at the BL01B1 of SPring-8 synchrotron radiation facility. The results showed that Cr was enriched and covered on the surface of the alloys during annealing and formed as Cr ₂O₃ or FeCr₂O₄. The phase and thickness of formed oxides depended on the alloy composition and the annealing conditions.