FeCrAl-based alloys containing gadolinium (Gd) are promising neutron-absorbing structural materials for spent nuclear fuel storage; however, the extremely low solubility of Gd in ferritic matrices promotes the formation of brittle Gd-rich phases, resulting in a fundamental trade-off between neutron absorption capability and mechanical reliability. In this study, high-loading (3.0 wt%) Gd₂O₃ oxide dispersion strengthened (ODS) FeCrAl alloys were developed to achieve high absorber density while preserving structural integrity. The comparative roles of Zr and Hf microalloying in oxide refinement and microstructural evolution were systematically investigated. Optimized high-energy mechanical alloying enabled homogeneous oxide dispersion under the high-oxide-fraction regime. Zr addition promoted fine, refined Zr–Gd–O complex oxides (∼20 nm) with high number density, whereas Hf addition resulted in coarser and chemically heterogeneous Gd-rich particles (∼34 nm). EBSD analysis revealed that the Zr-containing alloy developed a uniform recrystallized microstructure with low residual strain, while the Hf-containing alloy exhibited heterogeneous recrystallization and retained deformation substructures. Although both alloys exhibited comparable yield strengths (∼800 MPa at room temperature) due to dispersion strengthening, the Zr-containing alloy demonstrated significantly improved ductility and stable plastic deformation across the investigated temperature range. These results demonstrate that the morphological control and spatial uniformity of complex oxide dispersions—rather than grain refinement alone—govern the strength–ductility balance in high-Gd ODS FeCrAl alloys. These findings establish oxide refinement as the key design criterion for high-Gd ODS alloys and identify Zr microalloying as an effective strategy for achieving high absorber density while preserving mechanical reliability in neutron-absorbing structural materials.
Kim et al. (Mon,) studied this question.