Abstract: Engineering compositional fluctuations in refractory high-entropy alloys (RHEAs) is critical for next-generation structural materials. However, there remains a lack of understanding regarding composition-driven phase evolution and its role in deformation mechanisms. This study reveals the influence of spinodal structure on dislocation dynamics and resolves the strength-ductility trade-off in RHEAs. Hybrid molecular dynamics (MD) and Monte Carlo (MC) simulations indicate that Mo substitutional solid solution in the TiVHfNb system induces compositional segregation and spinodal-modulated phases. The Ti₄₁V₂₇Hf₁₃Nb₁₃Mo₆ RHEA achieves a yield strength of ∼1117 MPa and a ductility of ∼25.7 %, exhibiting a strength increase of ∼165 MPa compared to the base alloy without compromising ductility. With the addition of Mo, the increase in shear modulus enhances the solid solution strengthening effect, thereby elevating the yield strength. Slip trace analysis and TEM characterization reveal that Mo-assisted spinodal structure effectively promotes the activation of multiple slip systems and cross-slip behavior. On one hand, multi-slip facilitates frequent dislocation interactions and the formation of dislocation junctions, thereby enabling dynamic strain hardening. Stress relaxation tests further confirm that the spinodal structure plays a crucial role in retaining mobile dislocations, essential for sustaining plastic deformation. On the other hand, cross-slip initiated by the pinning effect mitigates strain localization, circumventing the conventional strength-ductility trade-off. This work provides critical insights for optimizing the mechanical properties of RHEAs.

Key words: Refractory high-entropy alloys, Spinodal structure, Mechanical properties, Deformation mechanism