The strongest size (original) (raw)

Nanocrystals

Nature volume 391, pages 532–533 (1998) Cite this article

How crystal grains deform in a material under stress is important both scientifically, for the understanding of plastic flow in solids, and technologically, for its direct effect on the material strength. Grain size plays an important part: in polycrystals with grain sizes in the micrometre range, strength increases with decreasing size. This is known as the Hall-Petch effect1,2, and was first explained in terms of the piling up of dislocations, created by the shearing of crystal planes in each grain, at the grain boundaries. As the grains become smaller, the effect of dislocation blocking increases, thereby strengthening the material. But with the synthesis of nanocrystals, with grains in the nanometre range, the opposite behaviour was found — specimens of copper and palladium softened with decreasing size3.

Why? As reported on page 561 of this issue4, computer simulations show that the reverse Hall-Petch effect arises primarily from sliding motions at grain boundaries. This is a timely demonstration of how materials simulations can now provide atomic-level insights into a wide range of physical phenomena.

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Figure 1: Variation of strength with grain size for metals.

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Authors and Affiliations

  1. the Nuclear Engineering Department, Massachusetts Institute of Technology, Cambridge, 02139, Massachusetts, USA
    Sidney Yip

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Yip, S. The strongest size.Nature 391, 532–533 (1998). https://doi.org/10.1038/35254

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