Oxidation performance of a Fe–13Cr alloy with additions of rare earth elements

The influence of rare earth elements (REEʹs) i.e. Neodymium (Nd) and Praseodymium (Pr) on the oxidation behavior of a Fe–13Cr alloy has been studied, and its role on the oxidation rate and oxide morphology and formation is discussed. Specimens were isothermally oxidized in oxygen at 800 °C for 24 h. It was found that a small addition (≤0.03 wt.%) of either Nd or Pr, reduced the oxidation rate of the Fe–13Cr base alloy. Moreover, the simultaneous addition of both elements to the alloy produced a dramatic reduction in the oxidation kinetics. Analysis by scanning electronic microscope (SEM) revealed that the morphology of oxides formed on Fe–13Cr specimens with and without REEʹs specimens was very different. In fact, a fine-grained oxide morphology was observed for alloys with REEʹs addition. For these alloys only, chromium enrichment at the metal/scale interface was observed. From transmission electronic microscope (TEM) analysis, it was found the following: at the early stages of oxide formation, after 0.25 h, Cr2O3, Fe3O4, α-Fe2O3 and γ-Fe2O3 were formed; at 6 h, Cr2O3, FeCr2O4 and α-Fe2O3 were identified and, for exposure times greater than 6 h, Cr2O3, α-Fe2O3 and a spinel which was presumably transformed into a solid solution (Fe2O3·Cr2O3) were found.