The key factor of low work hardening in nanostructured metals lies in an already saturated level of dislocation density which makes further storage and interplay of dislocations impossible during tensile deformation. Here we report a strategy to gain ductility by dropping first and then raising the dislocation density in a grain-size gradient nanostructure. The nanograins undergo the annihi-lation of high density dislocations followed by creation of mobile dislocations due to built-in mechanical incompatibility. As a result, a unique up-turn of the strain hardening rate successively occurs during tensile deformation, leading to high ductility in nanostructures.
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