Dual heterostructure construction via tailored nanoprecipitates for strength-ductility trade-off in ODS steels

Strength-ductility trade-off is a common issue in oxide dispersion strengthened (ODS) steels. Here, by designing oxide nanoparticles, a dual-heterostructure ODS-FeCrAl alloy has been developed to realize the combination of high strength and high ductility. The first level is heterogeneous oxide nanoparticles with different strengthening mechanisms, and the second level is heterogeneous zones with different grain sizes. The designed 0.5Y₂O₃ alloy achieves a perfect combination of ductility and strength at both room and high temperatures (650 °C) compared to a typical low Y₂O₃ ODS alloy (0.25Y₂O₃): nearly 20 % higher ductility at room temperature without any reduction in strength, and nearly 20 % higher ductility at high temperature with nearly 70 % higher strength. The optimal bimodal degree of the 0.5Y₂O₃ alloy and the coexistence of penetrable and impenetrable oxide nanoparticles play a dominant role in the strengthening-toughening effect. As the Y₂O₃ content increases, the fine Y₂Zr₂O₇ and Y₂Ti₂O₇ particles in ODS-FeCrAl alloys gradually transform into coarse, impenetrable YAl composite oxide particles. The beneficial effect of the bimodal structure on ductility is suppressed when the Y₂O₃ content exceeds 0.5 wt%, which is attributed to the premature failure of the ODS-FeCrAl alloy due to debonding of the unusually coarse YAl composite oxide nanoparticles during the deformation process. The effect of oxide nanoparticle properties on the thermal stability of ODS-FeCrAl alloys was also evaluated, and it was shown that the presence of a small fraction (∼26 %) of YAl composite oxide particles does not reduce the thermal stability of ODS-FeCrAl alloys.