Multi-Phase Design Strategy for Synergistic Strength–Ductility Optimization in V-Ti-Cr-Nb-Mo Refractory High-Entropy Alloys

Controlling multiple phases by adjusting elemental ratios and applying heat treatments effectively balances the strength and ductility of refractory high-entropy alloys. In this study, five types of V-Ti-Cr-Nb-Mo alloys were designed by varying the contents of V, Ti, and Nb, followed by annealing at 1200 °C for 8 h. The alloys' crystal structures, microstructure evolution, and mechanical properties were systematically investigated. The V-Ti-Cr-Nb-Mo alloys exhibited a typical dendritic structure with a dual-phase (BCC + HCP) matrix. When the Nb content was maintained at 35 at.% with increasing V content, the volume fraction of the HCP phase increased, and the C14 Laves phase emerged. The as-cast alloy V₁₅Ti₃₀Cr₅Nb₃₅Mo₁₅, with a triple-phase (BCC + HCP + Laves) structure, exhibited excellent mechanical properties, including a compressive strength of 1775 MPa and a ductility of 18.2%. After annealing, the HCP phase coarsened and partially dissolved, the Laves phase precipitation reduced, and while the hardness and strength decreased, the ductility improved significantly. The annealed alloy V₅Ti₃₅Cr₅Nb₄₀Mo₁₅, with a dual-phase (BCC + HCP) structure, achieved a ductility of 26.9% under a compressive strength of 1530 MPa. This work demonstrates that multi-phase refractory high-entropy alloys can significantly enhance the strength-ductility synergy, providing an experimental foundation for the compositional design and performance optimization of refractory high-entropy alloys.