Simultaneously Enhanced Strength and Fracture Resistance in HfNbTaTiZr Refractory High-Entropy Alloy at Higher Strain Rate

The effects of strain rate on tensile properties and fracture behavior of HfNbTaTiZr refractory high-entropy alloy (RHEA) were investigated. With the increase of strain rate in the range from 0.0001 to 0.1 s⁻¹, the yield strength increases from 740 to 825 MPa, demonstrating a strain rate sensitivity coefficient of 0.0173. Notably, while the uniform elongation diminished with rising strain rates, the fracture elongation of the RHEA remained constant at ~ 43%, suggesting an enhanced non-uniform elongation and an improved resistance to tensile fracture. Single-edge notch tension test further proves that the notch toughness increases at elevated loading rates. The complete work-hardening rate curves were plotted, and the work-hardening ability of the RHEA was found not decreasing significantly after necking, especially at high strain rate. The fracture of tensile samples across all the strain rates was dominated by void growth and coalesce, with dimples on the fracture surface being smaller at higher strain rates. This work reveals an unconventional increase in fracture resistance at higher strain rates, further indicating that ductile RHEAs may possess superior potential for use in structural applications subjected to high strain rate loading.