Strain rate dependence of heterogeneous deformation in a gradient-structured high entropy alloy

Unlocking the mechanical response and underlying mechanisms of gradient structures (GS) under high strain rates is critical for their applications in national defense and military sectors. This study presents the first systematic investigation into the impact mechanical response of gradient-structured high-entropy alloys (HEAs) coupled with B2 phases. Specifically, the gradient-distributed variations in dislocation density, stacking faults, and deformation twins were fabricated for a novel dual-phase Al₀.₃Si₀.₃CoCrFeNi HEA via the cyclic torsion technique. In comparison with homogeneous counterparts, the yield strength of the GS specimens was enhanced by 110.4 % while retaining a fracture elongation of 41.4 %. Subsequently, the GS specimens were subjected to compressive tests under a wide strain rate range of 10⁻⁴–10³/s. Unexpectedly, the GS specimens exhibited a distinct inverse gradient distribution of strain rate sensitivity (SRS)—a stronger SRS was observed at the central soft region, whereas a weaker SRS was detected at the edge hard region, realizing strength reversal within the heterogeneous regions of gradient structures. Strength reversal enables the alternating strain-bearing of these heterogeneous regions, thereby activating a sustainable dynamic strengthening mechanism.