Elucidating the role of Nb on the long-term uniform corrosion of FeCrAl alloy in a simulated PWR environment

As a nuclear fuel cladding candidate alloy, Nb-doped FeCrAl alloys demonstrate superior high-temperature strength compared to their Nb-free counterparts, attributed to a combination of solid solution strengthening and precipitation strengthening by Fe₂Nb-type Laves phase particles. However, prolonged exposure reveals a trade-off, as Nb-doped FeCrAl alloys exhibit reduced corrosion resistance. This manifests as greater weight loss, a thicker inner oxide layer, more severe spallation, and pronounced local corrosion along grain boundaries, which will pose significant risks to the integrity of fuel claddings. To understand these phenomena, a comprehensive study combining advanced microscopic characterization and first-principles calculations was conducted. Results indicate that Nb promotes the outward diffusion of Fe ions, accelerating oxide layer growth and compromising corrosion resistance. Paradoxically, Fe₂Nb-type Laves phase particles, provide localized protection to the underlying metal and significantly mitigate intergranular corrosion. These findings provide critical insights into the dual role of Nb in FeCrAl alloys, offering guidance for optimizing alloy design for applications in light water reactors and advanced nuclear reactors.