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Milan Ardeljan2 Manish Jain3 Siddhartha Pathak3 Nan Li4 Anil Kumar4 Shijian Zheng5 Kevin Baldwin4 Marko Knezevic2 Nathan Mara6 Irene Beyerlein1

2, University of New Hampshire, Durham, New Hampshire, United States
3, University of Nevada, Reno, Reno, Nevada, United States
4, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
5, Institute of Metals, Shenyang, Liaoning, China
6, University of Minnesota, Minneapolis, Minnesota, United States
1, University of California, Santa Barbara, Santa Barbara, California, United States

The goal of the work presented is to gain an understanding of the deformation mechanisms underlying the deformation of nanolayered composites containing either bcc and hcp Mg phases. Nanolayered composites comprised of 50% volume fraction of Mg and Nb were synthesized using physical vapor deposition with individual layer thicknesses h of 5 nm, 6.7 nm, and 50 nm. At the lower layer thicknesses of h = 5 nm and 6.7 nm, the Mg was found to have undergone a phase transition from HCP to BCC, such that it formed a coherent interface with the adjoining Nb phase. Micropillar compression testing normal and parallel to the interface plane showed that the BCC Mg composite is much stronger and can sustain higher strains to failure. Transmission electron microscopy and density functional theory calculations for the relative barriers to shear on crystallographic slip systems and Mg/Nb interface together suggest that the deformation is predominantly mediated by slip in the layers. A crystal plasticity model with the h-dependent critical resolved shear stresses was developed and applied to understand the linkage between the observed deformation response and underlying mechanisms. Calculations from the model predict that the stress-strain response results from dislocation mediated plasticity on the {110}and {112} slip systems.

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