An extraordinary enhancement of strain hardening in fine-grained zirconium

Grain refinement always leads to a high strength but a low ductility that results from a reduced strain hardening. Here, we report an extraordinary enhancement of strain hardening in fine-grained (FG) Zr with an average grain size of 2-3 μm compared with its coarse-grained (CG) counterpart, which yields a uniform elongation of ~15.5% in the same order as that (~13.2%) of the CG Zr. The unusually enhanced strain hardening in the FG Zr is attributed to the formation of nano-scale defect structures within the fine grains. The present work provides a promising way to enhance the ductility of fine- and ultrafine-grained materials without losing their high strength, and thus is of wide interest.