Corrosion Behavior of Ni–20Cr–18W–1Mo Superalloy in Supercritical Water

Abstract

The corrosion behavior of Ni–20Cr–18 W–1Mo superalloy in supercritical water 500 °C/25 MPa for 200 h is investigated using gravimetry, SEM/EDS, XPS, and TEM. The oxide films show a layered structure with Ni rich in the outer layer, and Cr rich in the inner layer, consisting of an outer Ni(OH)2 and NiO layer, including some Cr(OH)3, and an inner Cr2O3, NiCr2O4, and WO3 layer. Mo elements are not oxidized. The oxide films grow via a mixed mechanism, namely metal dissolution/oxide precipitation mechanism and solid-state growth mechanism. The effects of secondary and primary carbides on the weight-gain trend and oxide formation are discussed.