Deformation-induced amorphization and nanocrystallization in high-entropy alloys

High-entropy alloys (HEAs) with exceptional cryogenic strength and toughness are pivotal for extreme engineering applications, yet their deformation mechanisms at ultra-low temperatures remain incompletely understood. Here, we report two types of deformation-induced amorphization and nanocrystallization within amorphous bands in a CrMnFeCoNi HEA under tensile loading at 4.2 K. Unlike dislocation-driven amorphization that forms nanoscale amorphous bands (nano-ABs, >5 nm thick), supra-nanometer amorphous bands (SN-ABs, <5 nm thick) emerge via lattice distortion under extreme localized shear localization rather than dislocation accumulation. Concurrently, localized heating from plastic deformation triggers nanocrystallization within nano-ABs, generating randomly oriented nanograins. The amorphization and nanocrystallization are expected to provide an extra toughening mechanism for HEAs by dissipating strain energy and impeding shear localization. Crucially, we establish a microstructural link between low-temperature serrated flow behavior and thermo-mechanical instability: stress drops and strain bursts correlate with heat-induced phase transitions and nano-ABs/SN-ABs formations.