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Emergence of strain-rate sensitivity in Cu nanopillars: Transition from dislocation multiplication to dislocation nucleation

Jennings, Andrew T. and Li, Ju and Greer, Julia R. (2011) Emergence of strain-rate sensitivity in Cu nanopillars: Transition from dislocation multiplication to dislocation nucleation. Acta Materialia, 59 (14). pp. 5627-5637. ISSN 1359-6454.

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We demonstrate strain-rate sensitivity emerging in single-crystalline Cu nanopillars with diameters ranging from 75 up to 500 nm through uniaxial deformation experiments performed at different constant strain rates. In the range of pillar diameters and strain rates tested, we find that the size dependence of the pillar strength deviates from the ubiquitously observed power law to a relatively size-independent flow strength, markedly below the predicted theoretical strength for strain rates slower than 10^(−1) s^(−1). We find this transition diameter, D_t, to be a function of strain rate, where faster strain rates shift the transition diameter to smaller pillar diameters: D_t ~ 150 nm at 10^(−3) s^(−1) and D_t ∼ ≤75 nm at 10^(−1) s^(−1). We compute the activation volumes, Ω, as a function of pillar diameter at each strain rate and find that for pillar diameters below D_t, the activation volumes are relatively small, Ω < 10b^3. This range agrees favorably with atomistic simulations for dislocation nucleation from a free surface. We postulate a plasticity mechanism transition from dislocation multiplication via the operation of truncated dislocation sources, also referred to as single-arm sources, in pillars with diameters greater than D_t to dislocation nucleation from the surface in the smaller samples.

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Greer, Julia R.0000-0002-9675-1508
Additional Information:© 2011 Acta Materialia Inc. Published by Elsevier Ltd. Received 13 January 2011; received in revised form 13 May 2011; accepted 20 May 2011; Available online 21 June 2011. The authors gratefully acknowledge Wei Cai, Chris Weinberger and Ting Zhu for useful discussions. Further, we would like to thank Wei Cai and Chris Weinberger for the SAS atomistic image. A.T.J., J.L. and J.R.G. gratefully acknowledge the financial support of the National Science Foundation through A.T.J.’s NSF Graduate Research Fellowship, J.L.’s NSF CMMI-0728069 and J.R.G.’s CAREER Grant DMR-0748267.
Group:Kavli Nanoscience Institute
Funding AgencyGrant Number
NSF Graduate Research FellowshipUNSPECIFIED
Subject Keywords:Nanostructure; Copper; Theory; Compression test
Issue or Number:14
Record Number:CaltechAUTHORS:20110912-113911247
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:25297
Deposited By: Jason Perez
Deposited On:13 Sep 2011 18:07
Last Modified:03 Oct 2019 03:04

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