Oxidation behavior of a new Fe–Ni–Cr-based alloy in pure steam at 750 °C

Abstract

The isothermal oxidation of a new Fe–Ni–Cr-based alloy has been investigated in pure steam at 750 °C for exposure time up to 500 h using secondary electron microscope (SEM)/ X-ray energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Results showed that the alloy was oxidized approximately following a parabolic law with a parabolic rate constant kp of 2.36 × 10−13 g2/m4/s. As revealed by SEM/EDS and XRD results, a duplex-layered external oxide scale was formed, consisting of a thin outer layer of Ni(Fe, Al)2O4 and a thicker inner layer of (Cr, Mn)2O3. Underneath the external oxide scale, the internal oxidation of Ti to be TiO2 occurred particularly along the grain boundaries of the matrix alloy. Internal oxide of Al2O3 was also observed but at a deeper depth. Based on the detailed compositional and microstructural characterization of the oxidized zone, the mechanism of the external and internal oxidation in steam is presented.