Dynamic deformation behaviors and structure evolution of TiZrHf hexagonal closed-packed medium-entropy alloy

In this study, the deformation behavior of a hexagonal closed-packed (HCP) TiZrHf medium-entropy alloy (MEA) was investigated across a wide range of strain rates from 10⁻⁴ s⁻¹ to 4990 s⁻¹. The alloy exhibits an exceptional combination of strength and plasticity during dynamic loading, as well as a noticeable strain rate hardening effect. The strain rate hardening effect is associated with the strong dislocation drag resulting from the fast dislocation velocity at high strain rates. Microstructure evolution analyses demonstrate that various deformation mechanisms occur within shear bands under dynamic loading, including the formation of deformation twins, dislocation cells, microbands, amorphous bands, and dynamic recrystallization. The dynamic deformation is influenced by the competition between hardening mechanisms and thermal softening effects. Dislocations, deformation twins, and amorphous bands dominate the strain hardening effect, while temperature rise induced by adiabatic shear contributes to thermal softening effects. Additionally, dynamic recrystallization and amorphization also lead to a decrease in dislocation density during dynamic loading.