Strengthening and Deformation Mechanisms in Refractory High-Entropy Alloys: From Dislocation Motion to Strength–Ductility Synergy

Refractory high-entropy alloys (RHEAs) are promising candidates for ultrahigh-temperature structural applications because of their high melting temperatures and good strength retention at elevated temperatures. Their mechanical behavior, however, is governed by the competition between resistance to dislocation motion and plastic strain accommodation. This review examines the strengthening and deformation mechanisms of RHEAs from a dislocation-centered perspective. Solid-solution strengthening, chemical short-range order (CSRO), second-phase strengthening, and grain-boundary strengthening are discussed in terms of their effects on dislocation mobility. Dislocation slip, deformation twinning, transformation-induced plasticity (TRIP), dynamic recovery, and dynamic recrystallization are then reviewed, with emphasis on the roles of crystal structure, local chemical environment, phase stability, temperature, and strain rate. Heterogeneous structure design, metastability engineering, and coherent strain-field regulation are further discussed for improving the balance between strength, plastic strain accommodation, and work hardening. Overall, the mechanical response of RHEAs depends on the type, distribution, stability, and interaction of microstructural features with available deformation pathways. Key challenges include clarifying the effects of local chemical order on different dislocation modes, understanding deformation-mechanism transitions, and maintaining microstructural stability during prolonged high-temperature exposure.