Negative-curvature interfaces enable highly synergistic strength-ductility-toughness at 77 K

Precipitation hardening is a well-known strategy that can raise the yield strength of alloys to well over 1 GPa, including at 77 K, but is less potent in offering strain hardening than twinning/transformation-induced-plasticity (TWIP/TRIP) mechanisms, which have been essential for the high ductility and fracture toughness of established cryogenic alloys. Here we demonstrate an innovative strategy to tailor the coherent nanoprecipitates by purposely designing negative-curvature interfaces (NCIs). This morphological control uses the geometric curvature and curvature-gradient effects to generate additional local stress, high elastic energy density, and substantial strain gradients to make NCIs prolific sources of dislocation nucleation. The proliferation of partial dislocations builds up ultra-dense hierarchical stacking-faults dynamically all over the deforming volume, substantially enhancing strain-hardening and toughening. The resulting NiCoCrAlTa alloy exhibits excellent cryogenic mechanical properties, achieving a high yield strength of 1.26 GPa, a product (~90 MPa%) of ultimate tensile strength (~1.80 GPa) with tensile ductility (~50%) and a fracture toughness of 213 MPa·m1/2 at 77 K—representing a record-high combination among all reported alloys to date. Our interface design strategy may be applicable to all precipitation-hardened alloys, transforming the precipitates from merely passive strengtheners to active and tunable agents regulating the plastic flow. Here authors engineer coherent nanoprecipitates with negative-curvature interfaces in the NiCoCr-AlTa system, acting as prolific sources of dislocation nucleation and leading to enhanced cryogenic mechanical performance.