Comprehensive Analysis of Oxidation Mechanisms of Inconel 718 in Supercritical Water

Abstract

Inconel 718 is an age-hardenable (Ni-Fe-Cr-Nb-Mo-Ti-Al) superalloy widely used in gas turbines, rocket motors, spacecraft, nuclear reactors, pumps and tooling due to its excellent combination of oxidation resistance, tensile and creep properties and good weldability. This superalloy has also microstructural stability and resistance to strain-age cracking at elevated temperatures. Due to outstanding high-temperature properties of this alloy, several studies are ongoing to test its performance in other harsh environments. In the present investigation, the oxidation behavior of Inconel 718 exposed to supercritical water at 600 ºC and 25 MPa for 100, 300 and 1000 hours was investigated using gravimetry and scanning electron microscopy. Also, synchrotron-based X-ray absorption spectroscopy was employed to determine the oxidation states of Ni and Fe in the oxide layer formed after each step of oxidation test. Thus, detailed oxidation mechanism of the Inconel 718 in the supercritical water is proposed based on the obtained experimental data.