High strength and ductility in multimodal-structured Zr

Metals can be strengthened by many methods, but theses strategies always result in limited ductilities. A simultaneous enhancement of strength and ductility in metals is still a great challenge. In the present study, a multimodal grain structure composed of coarse grains (∼24%), ultrafine grains (∼56%), and nanoscale grains or subgrains (∼20%) has been introduced in hcp pure Zr by employing cryorolling in the temperature range from -160 to -90 °C combined with subsequent low-temperature annealing. The multimodal structured Zr exhibits a high ultimate tensile strength (∼658. MPa) and a large uniform elongation (∼8.5%) simultaneously. The high strength results from the contribution of nanoscale and ultrafine grains, while the improved ductility is mainly derived from the improved strain hardening capability by the coarse grains that are effective in storing dislocations and complex deformation strain paths caused by the multimodal distribution of grain sizes.