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The effect of size, orientation and alloying on the deformation of AZ31 nanopillars

Aitken, Zachary H. and Fan, Haidong and El-Awady, Jaafar A. and Greer, Julia R. (2015) The effect of size, orientation and alloying on the deformation of AZ31 nanopillars. Journal of the Mechanics and Physics of Solids, 76 . pp. 208-223. ISSN 0022-5096.

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We conducted uniaxial compression of single crystalline Mg alloy, AZ31 (Al 3% wt. and Zn 1% wt.) nanopillars with diameters between 300–5000 nm with two distinct crystallographic orientations: (1) along the [0001] c-axis and (2) at an acute angle away from the c-axis, nominally oriented for basal slip. We observe single slip deformation for sub-micron samples nominally oriented for basal slip with the deformation commencing via a single set of parallel shear offsets. Samples compressed along the c-axis display an increase in yield strength compared to basal samples as well as significant hardening with the deformation being mostly homogeneous. We find that the “smaller is stronger” size effect in single crystals dominates any improvement in strength that may have arisen from solid solution strengthening. We employ 3D-discrete dislocation dynamics (DDD) to simulate compression along the [0001] and [1122] directions to elucidate the mechanisms of slip and evolution of dislocation microstructure. These simulations show qualitatively similar stress strain signatures to the experimentally obtained stress-strain data. Simulations of compression parallel to the [1122] direction reveal the activation and motion of only <a>-type dislocations and virtually no dislocation junction formation. Computations of compression along [0001] show the activation and motion of both <c+a> and <a> dislocations along with a significant increase in the formation of junctions corresponding to the interaction of intersecting pyramidal planes. Both experiments and simulation show a size effect, with a differing exponent for basal and pyramidal slip. We postulate that this anisotropy in size effect is a result of the underlying anisotropic material properties only. We discuss these findings in the context of the effective resolved shear stress relative to the unit Burgers vector for each type of slip, which reveal that the mechanism that governs size effect in this Mg-alloy is equivalent in both orientations.

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Greer, Julia R.0000-0002-9675-1508
Additional Information:© 2014 Elsevier B.V. Received date: 14 May 2014. Revised date: 14 October 2014. Accepted date: 30 November 2014. Research was sponsored by the Army Research Laboratory and was accomplished under Cooperative Agreement Number W911NF-12-2-0022. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the Army Research Laboratory or the U.S. Government. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation herein. Authors ZHA and JRG also gratefully acknowledge the financial support of NSF (DMR-1204864). The authors also acknowledge the facilities and staff of the Kavli Nanoscience Institute at Caltech. The authors thank Dongchan Jang and Carol Garland for TEM assistance.
Group:Kavli Nanoscience Institute
Funding AgencyGrant Number
Army Research LaboratoryW911NF-12-2-0022
Subject Keywords:Nano-Compression Experiments; Discrete dislocation dynamics; Magnesium; Orientation effects; Size effects
Record Number:CaltechAUTHORS:20141208-085540326
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Official Citation:Zachary H. Aitken, Haidong Fan, Jaafar A. El-Awady, Julia R. Greer, The effect of size, orientation and alloying on the deformation of AZ31 nanopillars, Journal of the Mechanics and Physics of Solids, Volume 76, March 2015, Pages 208-223, ISSN 0022-5096, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:52454
Deposited By: Ruth Sustaita
Deposited On:09 Dec 2014 22:24
Last Modified:03 Oct 2019 07:42

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