Revealing Extraordinary Intrinsic Tensile Plasticity in Gradient Nano-Grained Copper

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Science  17 Feb 2011:
DOI: 10.1126/science.1200177


Nano-grained (NG) metals are believed to be strong but intrinsically brittle: Free-standing NG metals usually exhibit a tensile uniform elongation of few percent. When a NG Cu film is confined by a coarse-grained Cu substrate with a gradient grain size transition, tensile plasticity can be achieved in the NG film where strain localization is suppressed. The gradient NG film exhibits a 10 times higher yield strength and tensile plasticity comparable to the CG substrate and can sustain a tensile true strain exceeding 100% without cracking. A mechanical-driven grain boundary migration process with a significant concomitant grain growth dominates plastic deformation of the gradient NG structure. The extraordinary intrinsic plasticity of gradient NG structures offers their potential as advanced coatings of bulk materials.