Insight into a high temperature selective oxidation of HP40 alloy under a H2–H2O environment

Abstract

In the present work, a selective oxidation process of HP40 alloy at 1050 °C under a H₂–H₂O environment were studied in detail by means of SEM, EDS, GD-OES, XRD, Raman spectra and XPS. The results revealed that selective oxidation of Mn and Cr elements was realized, and the oxide scale preferentially grew via grain boundary rather than via grain lattice. The oxide scales were composed of a majority of MnCr₂O₄ spinel and a spot of Cr₂O₃ throughout the oxidation process. Mn existed in the form of Mn²⁺ ions on the surface, while Cr existed in various species. Metal hydroxides appeared on the surface approved by spectra of the O 1s region, and the relative amount of them decreased with oxidation time.