Cryogenic amplification of the HDI effect enhances strength-ductility synergy in layered heterostructures

The hetero-deformation-induced (HDI) hardening effect is crucial for overcoming the strength-ductility trade-off in heterostructured metals; however, its behavior at cryogenic temperatures remains unclear. Here, we examine the mechanical response of layered Cu/Fe samples at 293 K and 77 K, revealing a substantial enhancement in the synergy between strength and ductility at 77 K. Loading-unloading-reloading (LUR) tests indicate a stronger Bauschinger effect and a higher level of HDI stress at the cryogenic temperature. Microscopic characterizations reveal intensified strain partitioning and increased geometrically necessary dislocation (GND) accumulation near hetero-zone boundaries, which is attributed to a greater yield strength mismatch between Cu and Fe. Crystal plasticity finite element (CPFE) simulations further capture the enhanced strain partitioning, elevated GND density, and increased back stress at 77 K, consistent with experimental results. These findings demonstrate that cryogenic conditions significantly amplify the HDI effect, providing valuable insights for designing heterostructured materials suited for advanced cryogenic applications.