Dynamic creation and evolution of gradient nanostructure in single-crystal metallic microcubes

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Science  21 Oct 2016:
Vol. 354, Issue 6310, pp. 312-316
DOI: 10.1126/science.aag1768

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A shocking transformation for silver

Clever processing of metals leads to technologically useful properties such as increased hardness and ductility. Thevamaran et al. fired specially synthesized silver cubes at a hard piece of silica, which produced a shock wave that dramatically changed the microstructure of the silver. The approach produced an extreme range in grain sizes that is useful for creating bendable yet strong metals.

Science, this issue p. 312


We demonstrate the dynamic creation and subsequent static evolution of extreme gradient nanograined structures in initially near–defect-free single-crystal silver microcubes. Extreme nanostructural transformations are imposed by high strain rates, strain gradients, and recrystallization in high-velocity impacts of the microcubes against an impenetrable substrate. We synthesized the silver microcubes in a bottom-up seed-growth process and use an advanced laser-induced projectile impact testing apparatus to selectively launch them at supersonic velocities (~400 meters per second). Our study provides new insights into the fundamental deformation mechanisms and the effects of crystal and sample-shape symmetries resulting from high-velocity impacts. The nanostructural transformations produced in our experiments show promising pathways to developing gradient nanograined metals for engineering applications requiring both high strength and high toughness—for example, in structural components of aircraft and spacecraft.

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