Simultaneously achieving high mechanical properties and oxidation resistance of 9Cr ODS Fe-based superalloy at elevated temperature via Al and Si-alloying

Developing 9Cr oxide dispersion-strengthened (ODS) Fe-based superalloy combining elevated-temperature strength and oxidation resistance was a challenge for advanced nuclear applications. A new 9Cr ODS ferrite-martensite superalloy was designed via Al- and Si-alloying, aiming to improve the comprehensive performance at elevated temperatures. The microstructure, mechanical properties and oxidation resistance of 9Cr ODS superalloy were investigated in detail. 1.5Al1Si (1.5 wt% Al and 1 wt% Si) alloy achieved the simultaneous improvement of mechanical properties and oxidation resistance compared with other alloys at elevated temperatures. Multi-scale characterization revealed that the 1.5Al1Si alloy exhibited a refined dual-phase ferritic-martensitic structure (average grain size: 1.47 μm) with coherent Y₂Ti₂O₇ nanoparticles (8.9 ± 2.6 nm), enabling the high tensile strength (648 MPa) at 550 °C. Al and Si co-addition promoted the preferential formation of a continuous Cr₂O₃ layer after exposure to air at 850 °C for 200 h. Benefiting from the a concrete Cr₂O₃ protective layer, the oxide scale of 1.5Al1Si alloy did not spall, with the weight gain was only 0.79 mg/cm². Our work demonstrated that the Al and Si co-alloying was an effective way to improve the comprehensive performance of 9Cr ODS superalloy at elevated temperature.