Corrosion behavior and slow strain rate tensile testing of Inconel 718 alloy in deaerated supercritical water at 650 °C

The general corrosion and stress corrosion cracking behaviors of Inconel 718 alloy were investigated in deaerated supercritical water at 650 °C using corrosion kinetics analysis, microstructural characterization and slow strain rate tensile testing. The results show that the weight gain of 718 alloy initially increases, then decreases and finally increases again as corrosion time progresses. The initial weight gain is attributed to the formation of an oxide film composed of Cr 3 O 2 and spinel oxides on the surface. Then, the corrosion pits are formed due to the oxidation of niobium carbides and the subsequent detachment of Nb 2 O 5 , which causes weight loss. Over time, the oxide nodules with outer (Fe,Ni) 3 O 4 spinel layer, middle NiO layer and inner Cr 3 O 2 layer are developed at these pitting regions, leading to the reappearance of weight gain. Despite its excellent general corrosion resistance, the 718 alloy exhibits a high susceptibility to intergranular stress corrosion cracking in supercritical water environments.