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.

► A multimodal grain structure has been introduced into hcp pure Zr.
► The multimodal-structured Zr exhibits a high strength and a good ductility.
► It exhibits a higher toughness than that of coarse-grained Zr.
► The nanoscale and ultrafine grains in the material contribute to its high strength.
► The improved strain hardening capability is responsible for its good ductility.