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.

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

http://science.sciencemag.org/content/354/6310/312