Nanoscale defect engineering for enhanced dynamic performance in CrCoNi medium entropy alloy

The inherent lower yield strength of single-phase face-centered cubic (FCC) medium entropy alloys (MEAs) often limits their practical application, particularly in dynamic impact scenarios. This study investigates the dynamic compressive response of the CrCoNi MEA processed through sequential cryo-rolling. The cryo-deformed material exhibited an exceptionally high compressive yield and flow stress exceeding 2.25 GPa under dynamic loading, representing a remarkable 266 % increase compared to its as-cast counterpart. The observed amplification in yield and flow stress is attributed to a synergistic interplay between intrinsic nanoscale defects, introduced during cryo-deformation, and extrinsic defects that evolved during high-strain-rate loading. Post-deformation microstructural analysis revealed extensive twin-twin and stacking fault interactions, discrete dislocation configurations, abundant stacking fault canals, and localized atomic fluctuations within the matrix. The dynamic reactions between these intrinsic and extrinsic defects led to significant grain refinement, characterized by the formation of nanoscale prismatic segments. Specifically, the prismatic nanosegments and local chemical disorder contributed to elevated strength levels, while stacking faults and twins effectively accommodated strain compatibility and enhanced plasticity.