Gradient structure by SMAT. (A) Variation of average grain sizes along the depth. The error bars represent the SD of the grain sizes. The GS sample was produced by means of SMAT for 5 min on both sides of a CG IF-steel sheet. (B) Cross-sectional TEM bright-field image of the nanograins with a mean grain size of 96 nm at the depth of ?10 ?m. (C) Electron back-scatter diffraction image of coarse grains with a mean grain size of 35 ?m. Wu et al. (2014b) Click to enlarge.

Drawing inspiration from the structure of bones and bamboo, researchers at the Chinese Academy of Sciences (CAS) and North Carolina State University have found that by gradually changing the internal structure of metals to a gradient structure (GS), they can make stronger, tougher materials that can be customized for a wide variety of applications—from body armor to automobile parts.In a pair of open access papers, one published in the Proceedings of the National Academy of Sciences (PNAS), the other in Materials Research Letters, the researchers, led by Yuntian Zhu at NC State and Xiaolei Wu at CAS, report that gradient structures in engineering materials such as metals produce an intrinsic synergetic strengthening, which is much higher than the sum of separate gradient layers; the gradient structure renders a unique extra strain hardening, which leads to high ductility.