Enhanced strain rate hardening and phase transformation in body-centered cubic medium entropy alloy under dynamic deformation

In this study, we have studied the mechanical properties and microstructural evolution of Zr₅₀Ti₃₅Nb₁₅ body-centered cubic (bcc) medium-entropy alloy under dynamic loading. The yield strength increases approximately one-fold from 547 MPa to 995 MPa by increasing the quasistatic strain rates to the dynamic one, indicating a strong strain rate hardening. Furthermore, the strain rate sensitivity under dynamic loading is 0.099, which is eight times higher than that of quasistatic loading. Phase transformation from bcc to face-centered orthorhombic α″ occurs in the alloy after dynamic loading instead of quasistatic loading, and the volume of α″ phase increases with strain rates. The strong phonon drag effect and lattice friction enhance the resistance to dislocation motion under dynamic deformation, resulting in remarkable increase in yield strength. Moreover, the reduced activation volume due to local stress fluctuation and increased phase interface resulting from increasing strain rate are responsible for the high strain rate sensitivity.