Enrichment And Depletion Of Alloying Elements In Surface Layers Of Iron Base Alloys Annealed Under Different Conditions

X-ray photoelectron spectroscopy (XPS), electron microprobe microanalysis (EPMA), and secondary ion mass spectrometry (SIMS) have been used for analyzing the chemical composition in surface layers of iron-base alloys. Samples analyzed in this study were a ferritic Fe-Mn alloy annealed under low partial pressure of oxygen and an austenitic Fe-Mn-Si-Cr alloy annealed under vacuum. The XPS results showed that manganese was enriched and oxidized while iron was metallic in the surface layer of the Fe-Mn alloy annealed under a low partial pressure of oxygen. The EPMA results showed that manganese was depleted while chromium was enriched in the Surface layer of the Fe-Mn-Si-Cr alloy annealed under vacuum. The SIMS depth profiles coupled with the EPMA results indicated that the enrichment of chromium in the surface layer improves the oxidation resistance of the alloy. The enrichment and depletion of manganese in the surface layer is discussed on the basis of the thermodynamic properties of the iron-manganese system.