Precipitation-hardened refractoryTi-Nb-Hf-Al-Ta high-entropy alloys

This study reports the structure and mechanical properties of new refractory Ti_37.5Nb_12.5Hf₂₅Al₂₅, Ti₄₀Nb₃₀Hf₁₅Al₁₅, and Ti₄₀Nb₂₀Ta₁₀Hf₁₅Al₁₅ (at.%) high entropy alloys. After annealing at 1200 °C for 24 h, the program alloys had a single-phase B2 structure. Further annealing at 600 °C for 24 h resulted in the formation of Widmanstatten orthorhombic particles (O-phase) in the bcc matrix. The Ti₄₀Nb₃₀Hf₁₅Al₁₅ and Ti₄₀Nb₂₀Ta₁₀Hf₁₅Al₁₅ alloys annealed at T = 1200 °C showed moderate strength and good ductility (>50%) at 22 and 600 °C; while the Ti_37.5Nb_12.5Hf₂₅Al₂₅ alloy was stronger, but less ductile at both temperatures. Subsequent annealing at T = 600 °C significantly increased the strength of the Ti₄₀Nb₃₀Hf₁₅Al₁₅ alloy at 22 and 600 °C, maintaining compressive sufficient ductility at room-temperature.