Influence of secondary phases on the corrosion behavior of IN718 in high-temperature pressurized water

The corrosion behaviors of IN718 in a high-temperature pressurized water environment were investigated to assess the effect of secondary phases on the corrosion mechanisms. The oxide scale formed on IN718 after exposure to a 290 °C water environment consists of double layers: the outer layer is Fe 2 (Cr, Ni)O 4 spinel phase and the inner one is Cr 2 O 3 . The NbC inclusions located within the grains provide conducive sites for localized corrosion. Oxidation leads to the fragmentation of NbC particles, resulting in the formation of cavities on the surface. The Ni 3 Nb precipitates located at the grain boundaries exhibit a higher susceptibility to oxidation than the surrounding matrix. This preferential oxidation of the Ni 3 Nb precipitates effectively consumes the available oxygen atoms, thereby acting as a protective barrier that inhibits the propagation of oxidation along the grain boundaries. The oxidation of NbC and Ni 3 Nb phases initially occurs in an amorphous state and then transforms into a crystalline structure.