High Strength–Ductility Synergy of As-Cast B2-Containing AlNbTaTiZr Refractory High-Entropy Alloy Under Intermediate and Dynamic Strain Rates

Understanding the mechanical behavior of materials under various strain-rate regimes is critical for many scientific and engineering applications. Accordingly, this study investigates the strain-rate-dependent compressive mechanical behavior of B2-containing (TiZrNb)_79.5(TaAl)_20.5 refractory high-entropy alloy (RHEA) at room temperature. The RHEA is prepared by vacuum arc melting and is tested over intermediate (1.0 × 10⁻¹ s⁻¹, 1.0 s⁻¹) and dynamic (1.0 × 10³ s⁻¹, 2.0 × 10³ s⁻¹, 2.8 × 10³ s⁻¹, 3.2 × 10³ s⁻¹, and 3.5 × 10³ s⁻¹) strain rates. The alloy characterized as hybrid body-centered-cubic (BCC)/B2 nanostructure reveals an exceptional yield strength (YS) of ~1437 MPa and a fracture strain exceeding 90% at an intermediate (1.0 s⁻¹) strain rate. The YS increases to ~1797 MPa under dynamic strain-rate (3.2 × 10³ s⁻¹) loadings, which is a ~25 % improvement in strength compared with the deformation at the intermediate strain rate. Microstructural analysis of the deformed specimens reveals the severity of dislocation activity with strain and strain rate that evolves from fine dislocation bands to the formation of localized adiabatic shear bands (ASBs) at the strain rate 3.5 × 10³ s⁻¹. Consequently, the RHEA fracture features mixed ductile–brittle morphology. Overall, the RHEA exhibits excellent strength–ductility synergy over a wide strain-rate domain. The study enhances understanding of the strain-rate-dependent mechanical behavior of B2-containing RHEA, which is significant for alloy processes and impact resistance applications.