Microstructural Stability of Re- and Ru-Modified A2+B2 Refractory Compositionally Complex Alloys

Precipitation of B2 ordered particles is a promising option for extending the mechanical high-temperature capability of A2, refractory-element-based alloys. In the present work, 27.3Ta-27.3Mo-27.3Ti-8Cr-10Al (at.%) is taken as a reference alloy to which Re or Ru are added up to 5 at.% to determine how these additions affect precipitate formation, coarsening and elemental partitioning. Both additions increase B2 solvus and ordering temperatures, with 5 at.% Re and Ru raising the B2 solvus by 70 K and 50 K, respectively. During prolonged aging, Re and Ru also retard precipitate coarsening, with Ru resulting in a stronger effect at comparable concentrations. The two additions produce different precipitate morphology evolutions during aging. Precipitates in Re-containing alloys remain spherical, whereas Ru addition leads to plate-like and partially interconnected precipitates. Atom probe tomography reveals different trends in partitioning behavior. Re preferentially partitions to the A2 matrix while Ru exhibits only minor partitioning between A2 and B2. These results provide an alloy-design basis for extending the high-temperature capability of A2+B2 refractory alloys by increasing the solvus temperature and enhancing coarsening resistance. We gratefully acknowledge financial support from the Deutsche Forschungsgemeinschaft (DFG, grant no. HE 1872/34-2). Part of this work was carried out with the support of the Karlsruhe Nano Micro Facility (KNMFi, proposal no. 2025-034 032388), a Helmholtz Research Infrastructure at Karlsruhe Institute of Technology (KIT). LY acknowledges financial support from the China Scholarship Council (CSC, grant no. 202207000023). RJV acknowledges support from the Alexander von Humboldt Foundation. MM acknowledges financial support from the Landesgraduiertenförderung (LGF) of the State of Baden-Württemberg, Germany.