Microstructural analysis of preformed oxides on a zirconium alloy before and after subsequent oxidation at 1000–1200 °C

Highlights: • Microstructures of preformed oxides on a zirconium alloy were analysed by TEM. • Zr-Sn type precipitates were not observed after subsequent oxidation. • Many voids were formed after subsequent oxidation. • Many intergranular cracks were formed after subsequent oxidation at 1200 °C. - Abstract: Zr-1Nb-1Sn-0.1Fe alloy was pre-oxidised at 1200 °C and subsequently oxidised at 1012, 1100, and 1200 °C. The preformed oxide enhanced the oxidation resistance at 1012 and 1100 °C, but not at 1200 °C. The microstructures of the preformed oxides subsequently oxidised at 1200 °C were compared with those of the preformed oxides subsequently oxidised at 1012 and 1100 °C. The preformed oxide probably contained more intergranular cracks and liquid Sn precipitates, and less twin boundaries during the subsequent oxidation at 1200 °C. These microstructural differences may have caused the preformed oxide not to enhance the oxidation resistance at 1200 °C.