Refractory multi-principal element alloys with solution and aged HfRu-B2 precipitates

Ru-based B2 phases have shown promise as strengthening precipitates in refractory alloys due to their high (≥ 1600 °C) solvus temperatures. Of the Ru-based B2 phases, the HfRu-B2 phase is the most thermally stable and a solution and ageable BCC + HfRu-B2 alloy has yet to be reported. Three HfRu-containing refractory alloys were arc-melted and their phase equilibria investigated from 1300-1900 °C: Ta₃₀Mo₂₈Nb₂₂Hf₁₁Ru₉, Nb₅₂Mo₂₈Hf₁₁Ru₉, and Nb₅₂V₂₈Hf₁₁Ru₉ (at%). Scanning electron microscopy was used to characterize the microstructures after annealing. In all alloys, a HfRu-B2 phase was present as precipitates embedded in a disordered BCC phase. The HfRu-B2 phase was stable up to 1750 °C and additional Hf- and V-rich phases were stable at 1300 °C. After slow cooling, the HfRu-B2 precipitates in Nb₅₂V₂₈Hf₁₁Ru₉ evolved in morphology from spheres to cubes to cuboidal arrays with increasing aging time, characteristic of a low misfit between the HfRu-B2 and BCC phases.