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High strength and good ductility are essential for the applications of structural materials. However, the strength and ductility of materials are often mutually exclusive. For example, deformed materials always exhibit a hardening behavior, i.e. enhanced strength accompanied with reduced ductility. [1] This is attributed to the mutual entanglement and blockage of high-density dislocations induced by plastic deformation, which greatly inhibit the motion of dislocations. [2] Thermal annealing is indispensable for enhancing the ductility of deformed materials at the expense of their strength.Recently, studies show that dislocations in some special configurations are movable, which prevents localized shear deformation and contributes to the ductility of deformed materials. [3] To tailor dislocation configurations in deformed materials, high-density dislocations induced by plastic deformation are indispensable. This can be achieved by suppressing the dynamical recovery of deformed materials using cryogenic deformation that has been successfully employed to study lowtemperature properties of materials, [4] tailor their microstructures and mechanical properties. [5,6] More recently, our studies demonstrate strain rate has a significant effect on the dislocation configurations of cryorolled Zr, and the dislocations in lamella configurations are movable under high stress and contribute to plastic deformation. [7] Moreover, dislocation dynamics simulations show that in hcp Zr no dislocation junction forms between intersecting screw dislocations at low temperature, which results in a weak forest hardening. [8] These studies hint a work toughening behavior, not hardening behavior, may be observed in the hcp Zr if appropriate dislocation configurations, in which dislocations are moveable under high stress, are yielded through cryogenic deformation. To unambiguously confirm this supposition through experimentally procedure, both room temperature (RT) and cryogenic deformation experiments of metal Zr with increased strain were designed and performed in this study, and an extraordinary work toughening behavior is observed in the cryogenically deformed Zr, in contrast to the work hardening behavior of RT-cryorolled Zr. ExperimentalHigh-purity Zr (99.95%) sheets with a fully recrystallized microstructure (average grain size $30 mm) were rolled at RT and liquid nitrogen (LN) temperature at a strain rate of 2.63 s À1 with various strains e ¼ 0.5-2.95, respectively. The cryorolling was performed by immersing the samples into liquid nitrogen for 10 min before and after each rolling pass. The rolling temperature was determined to be À90 to À160°C by using both a Pt100 resistance thermometer and an adiabatic calorimeter. Cryorolled Zr sheets were annealed from 100 to 150°C for 1 h, and the annealed specimens were air-cooled to RT after annealing. The microstructure of cryorolled Zr in the RD-TD plane was characterized using a transmission electron microscope (TEM) and an X-ray diffractometer (XRD) with Cu Ka radiation. Dislocation densi...

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