Corrosion behaviour of Inconel 625 in hydrothermal phosphate molten salts in supercritical water

摘要

Nickel-based alloys are one of the best reactor materials for SCWO due to their excellent mechanical strength, resistance to pitting, creep, high temperature and stress corrosion cracking, but they are still susceptible to material failure in a number of complex environments, so this paper presents a comparative study of the corrosion behavior of Inconel 625 in supercritical water at various oxygen levels and phosphate phases. The study reveals that the oxide film formed after corrosion consists of three different layers. The outer layer is formed by outward diffusion of metal cations, the middle layer is a metal phosphate passivation layer, which blocks the diffusion of Fe, Ni, etc., and the inner layer is formed by inward oxidation of oxygen ions, which compete with oxygen ions in the dissolved phase phosphate. Molten phosphates facilitate the dissolution of the oxide film and the subsequent conversion of Cr 2O3 to soluble Cr3+, a process that is intensified by the presence of oxygen. In oxygen -free and oxygenated phosphate molten salt settings, oxide growth is dominated by the dissolution-precipitation mechanism. However, in the presence of dissolved -phase oxygenated phosphates, oxide formation is primarily controlled by the solid -phase growth mechanism.