Abstract
Molecular-dynamics simulations have recently been used to elucidate the transition with decreasing grain size from a dislocation-based to a grain-boundary-based deformation mechanism in nanocrystalline f.c.c. metals. This transition in the deformation mechanism results in a maximum yield strength at a grain size (the 'strongest size') that depends strongly on the stacking-fault energy, the elastic properties of the metal, and the magnitude of the applied stress. Here, by exploring the role of the stacking-fault energy in this crossover, we elucidate how the size of the extended dislocations nucleated from the grain boundaries affects the mechanical behaviour. Building on the fundamental physics of deformation as exposed by these simulations, we propose a two-dimensional stress-grain size deformation-mechanism map for the mechanical behaviour of nanocrystalline f.c.c. metals at low temperature. The map captures this transition in both the deformation mechanism and the related mechanical behaviour with decreasing grain size, as well as its dependence on the stacking-fault energy, the elastic properties of the material, and the applied stress level.
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Acknowledgements
V.Y., D.W. and S.R.P. are supported by the US Department of Energy, BES-Materials Science under contract W-31-109-Eng-38. V.Y. is also grateful for support from the DOE/BES Computational Materials Science Network (CMSN). A.K.M. acknowledges support from NSF-DMR. We are grateful for grants of computer time on the Cray-T3E at the John-von-Neumann-Institute for Computing in Jülich, Germany, and on the Chiba City Linux cluster at Argonne National Laboratory.
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Yamakov, V., Wolf, D., Phillpot, S. et al. Deformation-mechanism map for nanocrystalline metals by molecular-dynamics simulation. Nature Mater 3, 43–47 (2004). https://doi.org/10.1038/nmat1035
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DOI: https://doi.org/10.1038/nmat1035