Mechanical properties of nanocrystalline materials

When a crystal deforms plastically, phenomena such as dislocation storage, multiplication, motion, pinning, and nucleation occur over the submicron-to-nanometer scale. Here we report measurements of plastic yielding for single crystals of micrometer-sized dimensions for three different types of metals. We find that within the tests, the overall sample dimensions artificially limit the length scales available for plastic processes. The results show dramatic size effects at surprisingly large sample dimensions. These results emphasize that at the micrometer scale, one must define both the external geometry and internal structure to characterize the strength of a material.

http://science.sciencemag.org/content/sci/305/5686/986.full.pdf

Sample dimensions influence strength and crystal plasticity.

Hall-Petch relation and boundary strengthening

[Lu, L.; Chen, X.; Lu, K.] Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China. [Huang, X.] Tech Univ Denmark, Riso Natl Lab Sustainable Energy, Ctr Fundamental Res Met Struct Four Dimens, Dept Mat Res, DK-4000 Roskilde, Denmark.;Lu, L (reprint author), Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China;llu@imr.ac.cn

http://science.sciencemag.org/content/sci/323/5914/607.full.pdf

Revealing the Maximum Strength in Nanotwinned Copper

Overview of constitutive laws, kinematics, homogenization and multiscale methods in crystal plasticity finite-element modeling: Theory, experiments, applications

An attempt is made here to explain the observed phenomena in the yielding and ageing of mild steel, described in two previous papers, in the general terms of a grain-boundary theory. On this hypothesis, a satisfactory explanation of the variation of the lower yield point with grain size may be developed. It is shown that strain-ageing must involve two processes: a healing of the grain-boundary films, coupled with a hardening in the grains themselves. A discussion of the possible nature of the grain-boundary film is also undertaken.

https://iopscience.iop.org/article/10.1088/0370-1301/64/9/303/pdf

E O Hall

Papers

The Deformation and Ageing of Mild Steel: III Discussion of Results