Oxidation Mechanism of T91 and TP347H in Supercritical Water

This study addresses oxide scale spallation on boiler tubes in power plants, focusing on TP347H and T91 alloys as primary boiler tube materials. Oxidation tests were conducted to investigate the growth mechanism of oxide films, particularly emphasis on formation dynamics in supercritical water environments. High-temperature oxidation experiments were performed at 600 ℃ and 620 ℃ under supercritical water conditions. Using X-ray diffraction (XRD) and scanning electron microscope (SEM), we analyzed oxidation kinetics, oxide film microstructures, and elemental distributions. Results reveal significant differences between TP347H and T91:TP347H exhibits lower oxidation rates due to its higher Cr content, which facilitates formation of protective Cr-rich oxide layers. However, Cr₂₃C₆ precipitation at austenite grain boundaries predisposes this alloy to intergranular corrosion. Conversely, T91 demonstrates faster oxidation kinetics, forming porous oxide scales predominantly composed of Fe₃O₄ and Fe-Cr spinel. These scales exhibit poor adhesion and spall readily under thermal stress due to insufficient Cr content to form continuous Cr₂O₃ protective layers, enabling outward ferric inos diffusion that generates brittle oxides.