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 k_p 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.

Keywords:

• Alloy
• Advanced ultra-supercritical power plants
• High temperature
• Steam
• Oxidation
• SEM
• XRD

Funding

This work was supported by the National Natural Science Foundation of China (NSFC), [grant number 51401163], [grant number 51301130]; China Huaneng Group; Huaneng Power International, Inc.