A “high-entropy + dilute” design strategy delivers a strong and ductile refractory alloy from 77 to 1,373 K

Refractory high-entropy alloys (RHEAs) are ideal for extreme-temperature structural applications, but strengthening single-phase body-centered cubic (BCC) RHEAs typically compromises ductility, and systematic optimization across their vast compositional space remains challenging. In this work, we introduce a "high-entropy + dilute" design strategy that integrates concentrated high-entropy matrices with targeted dilute microalloying. We further refine this concept into an opposite-eigenstrain solute-pairing rule, in which solutes with opposite-sign local volumetric strains are combined to cooperatively amplify lattice distortion. Specifically, adding 1.5 at.% substitutional Re (local contraction) and 0.3 at.% interstitial B (local expansion) cooperatively amplifies local lattice distortion by approximately 20%, while maintaining a chemically homogeneous single-phase solid solution. This strategy raises the room-temperature yield strength by more than 34% while maintaining ductility, with the strength advantage sustained across an unusually wide temperature range from 77 to 1,373 K. Mechanistically, the amplified lattice distortion simultaneously modifies kink-pair-mediated screw glide and strengthens solute pinning of edge segments, thereby reducing screw-edge mobility mismatch and promoting coordinated dislocation multiplication and storage. These findings establish opposite-eigenstrain solute pairing as a mechanistically grounded microalloying strategy for strengthening single-phase BCC RHEAs across extreme temperatures.