Hf-induced transition in deformation mechanism enhances dynamic performance of NbTaTiZr refractory high-entropy alloy

• Hf changes NbTaTiZr deformation from twinning to dislocation slip. • Multi-scale kink bands dissipate energy, suppressing shear instability. • Rising stacking fault energy (607 → 700 mJ/m 2 ) suppresses twinning. • Mechanism bridges simulations and experiments to explain enhancement. This study presented a comprehensive investigation of the dynamic mechanical behavior and microstructural evolution of two refractory high-entropy alloys (RHEAs), NbTaTiZr and HfNbTaTiZr, under high-strain-rate compression using Split Hopkinson Pressure Bar (SHPB) tests. Through an integrated experimental and simulation approach, we elucidated the pivotal role of Hf in enhancing dynamic deformation resistance and suppressing catastrophic failure. Macroscopic analysis revealed that NbTaTiZr underwent severe shear localization and fracture at strain rates ≥ 5000 s −1 , characterized by adiabatic shear band (ASB) formation and mixed ductile–brittle fracture modes. In contrast, HfNbTaTiZr maintained remarkable structural integrity even at 6000 s −1 , exhibiting homogeneous plastic deformation and minimal radial expansion. Microstructural characterization via EBSD and TEM demonstrated that Hf addition promoted the formation of multi-level kink bands and hierarchical shear band networks, which effectively dissipated strain energy and delayed instability. Molecular dynamics simulations further revealed that Hf increased the generalized stacking fault energy (GSFE) from 607 mJ/m 2 to 700 mJ/m 2 , shifting deformation mechanisms from twinning-dominated to cross-slip and climb-controlled processes. These findings provided critical insights into the design of next-generation refractory high-entropy alloys for extreme dynamic environments, highlighting the efficacy of Hf alloying in enhancing mechanical performance through tailored dislocation dynamics and energy dissipation mechanisms.