Dynamic compression behavior of TiZrNbV refractory high-entropy alloys upon ultrahigh strain rate loading

In this study, the dynamic compressive response behavior of a body-centered cubic (BCC) single-phase TiZrNbV refractory high-entropy alloy (RHEA) was investigated under impact at speeds of 313–1584 m s–1 using two-stage, gas-gun-driven, high-speed plate-impact experiments; recovery sample analysis; and theoretical calculations. The strain rate and pressure were approximately 107 s−1 and 5.07–29.37 GPa, respectively. The results showed that the TiZrNbV RHEA had a Hugoniot elastic limit of 4.12–5.86 GPa and a spall strength of 1.84–2.03 GPa. The initial yield strength of the alloy showed a strong strain-rate dependence and could be described by the modified Zerilli–Armstrong model, while the phonon-damping effect was the main reason for its high strain-rate sensitivity. Microstructural analysis showed that the dynamic deformation of the TiZrNbV RHEA was controlled by the dislocation slip, dislocation proliferation, intersection of the deformation bands, and grain refinement. The analysis also showed that the intergranular, transgranular, and mixed-type cracks dominated the spall failure of the material. The dynamic Hall–Petch effect and pinning from the lattice distortion led to high dynamic yield strength. The critical strain rate for the phonon drag effect was positively related to the relative atomic mass and local strain field of the metals. Within the experimental loading range, the RHEA showed good structural stability, and simultaneously, the theoretical calculation method for the equation of state based on a cold-energy mixture could accurately predict its shock-response behavior. The valence-electron concentration (VEC) had a direct effect on the shock-compression properties of the HEAs; higher VEC implied more difficulty in compressing the HEAs. The findings of this study provide insights into understanding the mechanical response characteristics of RHEAs under extreme conditions such as high-speed impact and ultrahigh strain-rate loading.