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      Heterogeneous materials: a new class of materials with unprecedented mechanical properties

      1 , 2 , 3 , 4
      Materials Research Letters
      Informa UK Limited

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          Most cited references53

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          Ultrahigh strength and high electrical conductivity in copper.

          Methods used to strengthen metals generally also cause a pronounced decrease in electrical conductivity, so that a tradeoff must be made between conductivity and mechanical strength. We synthesized pure copper samples with a high density of nanoscale growth twins. They showed a tensile strength about 10 times higher than that of conventional coarse-grained copper, while retaining an electrical conductivity comparable to that of pure copper. The ultrahigh strength originates from the effective blockage of dislocation motion by numerous coherent twin boundaries that possess an extremely low electrical resistivity, which is not the case for other types of grain boundaries.
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            The deformation of plastically non-homogeneous materials

            M F Ashby (1970)
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              High tensile ductility in a nanostructured metal.

              Nanocrystalline metals--with grain sizes of less than 100 nm--have strengths exceeding those of coarse-grained and even alloyed metals, and are thus expected to have many applications. For example, pure nanocrystalline Cu (refs 1-7) has a yield strength in excess of 400 MPa, which is six times higher than that of coarse-grained Cu. But nanocrystalline materials often exhibit low tensile ductility at room temperature, which limits their practical utility. The elongation to failure is typically less than a few per cent; the regime of uniform deformation is even smaller. Here we describe a thermomechanical treatment of Cu that results in a bimodal grain size distribution, with micrometre-sized grains embedded inside a matrix of nanocrystalline and ultrafine (<300 nm) grains. The matrix grains impart high strength, as expected from an extrapolation of the Hall-Petch relationship. Meanwhile, the inhomogeneous microstructure induces strain hardening mechanisms that stabilize the tensile deformation, leading to a high tensile ductility--65% elongation to failure, and 30% uniform elongation. We expect that these results will have implications in the development of tough nanostructured metals for forming operations and high-performance structural applications including microelectromechanical and biomedical systems.
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                Author and article information

                Journal
                Materials Research Letters
                Materials Research Letters
                Informa UK Limited
                2166-3831
                June 25 2017
                November 15 2017
                June 26 2017
                November 15 2017
                : 5
                : 8
                : 527-532
                Affiliations
                [1 ] State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing, People’s Republic of China
                [2 ] School of Engineering Science, University of Chinese Academy of Sciences, Beijing, People’s Republic of China
                [3 ] Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC, USA
                [4 ] Nano Structural Materials Center, School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing, People’s Republic of China
                Article
                10.1080/21663831.2017.1343208
                b94ba1de-198c-4818-8b20-aa69b7eda6af
                © 2017

                http://creativecommons.org/licenses/by/4.0/

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