Martensitic transformation offers a pathway to overcome the room-temperature brittleness of refractory high-entropy alloys (RHEAs). The resulting extensive formation of the hexagonal close-packed (hcp) α-martensite necessitates deformation coordination via twinning to sustain plasticity during mechanical loading. However, the synergistic formation of multiple twin types and their effect on work hardening remain unclear. Employing advanced characterization techniques, this study identifies three primary martensitic twin systems ({ \(10\bar{1}1\) }, { \(10\bar{1}2\) }, and { \(13\bar{4}1\) }), two secondary twin configurations ({ \(10\bar{1}1\) }-{ \(13\bar{4}1\) } and { \(13\bar{4}1\) }-{ \(10\bar{1}1\) }), and three { \(13\bar{4}1\) } twin variants in metastable Ti27Zr40Hf23Ta10 RHEAs. The presence of multiple martensitic twins generates dense twin interfaces that refine the grain structure while effectively hindering dislocation motion, thereby enhancing strain hardening capacity. The coexistence of multiple martensitic twins increases the number of independent slip systems within grains and induces variations in slip systems across different regions of the grains. This heterogeneity in slip systems accommodates multi-directional plastic deformation, consequently improving the material's sustained hardening capability. These findings underscore the critical role of synergistic twinning mechanisms in governing the work hardening of metastable martensitic RHEAs.
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