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) Al 0.3 CoCrFeNi 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 b 3 , b = Bureger's vector), diminishing to 22-46 b 3 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 Al 0 . 3 CoCrFeNi.