FeMnSiCrNi Oxidation at 800 °C: Mechanism and Characterization of Improved Oxidation Resistance Generated by Vacuum Annealing Treatment

The oxidation resistance of an FeMnSiCrNi alloy was recently improved by vacuum heat treatment. However, a detailed characterization was still necessary to understand the effects of the treatment on the material structure and on the oxide evolution. This was the aim of the present study. Samples were vacuum annealed at 1100 °C for 10 h and the material volatilized was characterized by EDS/XRD; cross-sections were evaluated by SEM/EDS while surface analyses involved SEM/EDS, XPS and Raman. Oxidation exposures were performed after vacuum annealing for 1, 5, 10 and 24 h at 800 °C and the oxides were characterized by SEM/EDS, XRD, Raman; TEM-ASTAR and XPS were used after 1-h oxidation. The results demonstrated that vacuum annealing increases significantly the superficial roughness and that besides CrO formation, Mn incorporation in the oxide layer increased with the test duration, forming MnCrO and then MnO. Finally, silica was also observed at the metal/oxide interface.