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Mechanical Properties of Heterogeneous Nanostructured Metals



Mechanical behaviors of polycrystalline metals with nano-sized grains, or called as nano-grained or nanocrystalline metals, have been extensively investigated for several decades after the pioneering study of H. Gleiter in 1980s. However, measured mechanical properties of the metals with homogeneous nano-sized grains are rather disappointing: very high strength accompanied with very limited ductility. It means the traditional strength-ductility trade-off still holds in the homogeneous nanostructures. In recent years, several types of heterogeneous nanostructured metals with hierarchical structures have been synthesized. It is interesting to find that extremely high strength can be obtained without compromising tensile ductility or fracture toughness in the heterogeneous nanostructured metals. For instance, in a tempformed low-alloy steel containing ultrafine elongated ferrite grains strengthened with nano-sized carbides, toughness increases along with an increasing strength when temperature decreases from 60 to –60°C. Nano-twinned metals provided an alternative example of hierarchical nanostructured metals with extraordinary mechanical behaviors: strength is elevated to 10 times higher than that of coarse-grained form, accompanied with an obvious increased ductility

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