Ultrahigh Strength and Exceptional Work Hardening in a Hierarchical-Structured Alloy via Hetero-Interface-Mediated Twinning.

Yield strength and work hardening are two critical mechanical properties of metallic structural materials. However, increasing yield strength through conventional strengthening mechanisms often restricts further dislocation multiplications and interactions, which significantly reduces work hardening and poses a challenge to achieving an optimal balance between these properties in material design. Here, an innovative approach to simultaneously enhance both yield strength and work hardening in a heterostructured, nanoprecipitation-strengthened alloy is reported. This alloy exhibits an exceptional combination of a yield strength exceeding 1.5 GPa and an ultrahigh work hardening rate of 6 GPa, resulting in an extremely high tensile strength of 2.2 GPa and a uniform ductility of 20%. The ultrahigh yield strength primarily stems from nanoprecipitates and ultrafine grains, while the exceptional work hardening mainly originates from hetero-interface-mediated twinning. The hetero-deformation between the coarse-grained and ultrafine-grained regions results in dislocation pile-ups and strain gradients near the interfaces, which provides the ultrahigh stress necessary to activate mechanical twinning, thereby substantially improving the work hardening and plastic deformation stability of the alloy. The hetero-interface architecting strategy can potentially be applied to numerous other alloys, paving the way for designing novel materials with unprecedented mechanical properties for technological applications.