General corrosion and stress corrosion cracking behaviors of Alloy 825 in high-temperature supercritical water

General corrosion and stress corrosion cracking behaviors of Alloy 825 were investigated in supercritical water at 550 degrees C and 650 degrees C. The results show that Alloy 825 demonstrates consistent weight gain with prolonged exposure at 650 degrees C, while exhibits alternating weight gain and weight loss behaviors at 550 degrees C due to the interplay between uniform corrosion and pitting corrosion caused by the oxidation of TiN precipitates. At 550 degrees C, a porous and double-layer oxide film is generated, with the outer layer primarily composed of (Cr,Fe)2O3 grains and the inner layer consisting of the sub-layer matrix interspersed with polycrystalline spinel oxides. Stress corrosion cracking at this temperature is characterized by intergranular cracks at the edge regions of the fracture surface. At 650 degrees C, the oxide film is more uniform, compact and protective, comprising polycrystalline spinel oxides and Cr2O3. The fracture mode at this elevated temperature transitions to a combination of cleavage and ductile fractures.