High fracture toughness in a hierarchical nanostructured zirconium

Nanocrystalline metals usually exhibit a high strength but a disappointingly low ductility and toughness, which limit their practical utility. Here, we report a high fracture toughness (KIC~117 MPa m1/2) in a hierarchical nanostructured Zr that consists of nano-, sub-micrometer- and micrometer-sized grains, which is much larger than that KIC~78 MPa m1/2 in coarse-grained Zr. This hierarchical nanostructured Zr shows a good combination of yield strength (σs~550 MPa) and fracture toughness as compared with its coarse-grained counterpart. We expect that these results will have implications in the enhancement of fracture toughness of nanocrystalline materials and in the design of high-performance structural materials.