| Abstract Scope |
Tensile creep properties of Nb₄₅Ta₂₅Ti₁₅Hf₁₅, NbTaTi, and NbTaTiV refractory high-entropy alloys (RHEAs) were investigated under constant true stresses in high vacuum. Long-term thermal exposure revealed BCC metastability, with Group IV elements (Ti, Hf) exhibiting phase separation at grain boundaries, particularly in the presence of interstitial impurities (O, N). In non-V-containing alloys, high-temperature deformation was governed by screw dislocation glide, primarily via cross-kink collision and jog-dragging mechanisms, consistent with the Rao-Suzuki model. In contrast, NbTaTiV showed signs of edge dislocation glide control, likely due to V-induced local lattice distortion, enhancing interactions with edge dislocations. Both dislocation mechanisms are strongly thermally activated, as the high-temperature strength at 1173 K remains limited in single-phase NbTaTi-based RHEAs. These findings highlight the need for multiphase alloy design to achieve a better balance between high-temperature strength and room-temperature ductility in RHEAs. |