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Investigating the mechanics and deformation in multi-layered copper and niobium nanowires using atomistic simulations
Thesis   Open access

Investigating the mechanics and deformation in multi-layered copper and niobium nanowires using atomistic simulations

Dana Jaclynn Bronen
Master of Science (M.S.), Drexel University
Jun 2016
DOI:
https://doi.org/10.17918/etd-6915
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Abstract

Nanowires Materials Science Nanostructured Materials
This thesis employed atomistic simulations to investigate the role of layer thickness in multi-layered metallic nanowires. Nanowires are of great interest due to their unique mechanical properties and deformation mechanisms. The mechanisms controlling nanowire deformation are highly dependent on the volume fraction and interface orientation between materials within these structures. The behavior all of these variables have on nanowires still widely unknown. Experimental research has not been investigated greatly because of the difficulty, expense and time consuming nature of the fabrication and testing processes. It has been shown that atomistic simulations can probe these fundamental questions while providing vital insight on deformation mechanisms. Therefore, the work performed will exploit atomistic simulations to investigate the deformation mechanisms associated with multi-layered copper and niobium metallic nanowires. An embedded atom method potential was used during molecular statics to generate the alternating face-centered cubic and body-centered cubic interface. The potential was later employed during molecular dynamics compression simulations to accurately portray the behavior of individual atoms. These structures are first molded into nanowire structures before deformation at 10K under uniaxial compression at a constant strain rate to evaluate the role of layer thickness and interface. The presence of interfaces (e.g., grain boundaries and free surface), and their role in dislocation nucleation within confined volumes (i.e., nanowires) was then evaluated. Additionally, nanolaminate simulations with identical compositions were compressed using the same parameters to provide a comparison to structures without free surfaces. The simulation data was later applied to provide insightful results on atomic scale deformation. Plastic deformation mechanisms common to nanowires and nanolaminates were analyzed with various metric criteria. The unique deformation mechanisms within each layer and the interaction with the interface drove the compression response. Deformation induced dislocation movement and twin boundary development were specific to individual material layers. Therefore, these mechanisms were responsible for the differing material properties across all combinations. Finally, the rule of mixtures was evaluated to determine whether the unique nanoscale mechanisms were accounted for in the hypothesized material properties.

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