Microstructure and composition evolution of SPPs in the oxide film of Zr-1.0Sn-0.25Nb-0.2Fe-0.1Cr during corrosion

• Locally separated crystalline oxides of Fe, Cr and Zr are detected in the oxidized SPPs. • Fe has a faster depletion rate than Cr during the oxidation of the SPPs, and Nb seems to be almost immobile. • Some oxidized SPPs leave porous regions within the oxide film locally in the later stage. • The t-ZrO 2 is observed occasionally nearby the oxidized SPP in the outer layer of the oxide film. The microstructure and composition evolution of SPPs in the oxide film of Zr-1.0Sn-0.25Nb-0.2Fe-0.1Cr alloy during aqueous corrosion at 360 °C is investigated by HRTEM. The results show that SPPs with their distances to the O-M interface less than 500 nm remain metallic and exhibit similar structure and composition as those in Zr matrix. However, the SPPs with their distances to the O-M interface more than 1 μm exhibit obvious oxidation, characterized by the high O content and the appearance of the oxides of Fe, Cr and Zr inside the SPPs. The cracks connected to the SPPs could provide a good O supply and enhance the oxidation of the SPPs. Such cracks also promote the outwards diffusion of Fe and Cr from the SPPs during oxidation. In the oxidized Zr(FeCrNb) 2 particles, Fe has a faster outwards diffusion rate than Cr, while Nb seems to be almost immobile. Under certain conditions, small oxidized SPPs will leave porous regions within the oxide film locally. Tetragonal ZrO 2 is observed occasionally nearby the oxidized SPPs, which is thought to be caused by the doping effect of Fe depleted from the dissolved SPPs.