Dynamic Strain Aging and Negative Strain Rate Sensitivity in Coarse-grained Al0.3CoCrFeNi High Entropy Alloy Under Hot Compression

This study investigates the deformation behavior of coarse-grained (CG) Al0.3CoCrFeNi alloy under hot compression, revealing notable strain rate sensitivity (SRS) and dynamic strain aging (DSA) phenomena. DSA is observed at temperatures between 1223 K and 1373 K, exclusively at lower strain rates (0.5 s-1 – 1 s-1), while higher strain rates (≥ 5 s-1) exhibit DSA absence. Non-compact {112} slip activation on dislocation forest structures is proposed as the driving force behind DSA. Negative SRS behavior at 1223 K is attributed to Ni-Al cluster-based solid solution strengthening. Activation energy calculations highlight lattice diffusion and partial dislocation constriction as contributors to hot deformation. Consistency is observed in the activation volume (V*) calculation, indicating dislocation forest formation (127 – 519·b3, b = Bureger's vector), diminishing to 22 – 46·b3 upon DSA initiation. The alloy displays delayed dislocation hardening/softening transition due to CG's impact on retarding dislocation accumulation. This behavior stems from a higher V* at yielding, prolonging the typical transition observed in fine-grained alloys with lower V*. The study elucidates the intricate interplay of microstructure, strain rate, and deformation mechanisms in CG Al0.3CoCrFeNi.