UVM Theses and Dissertations
Format:
Print
Author:
Afanasyev, Konstantin A.
Title:
Dept./Program:
Physics
Year:
2007
Degree:
MS
Abstract:
Metallic nanowires with either single crystal or twinned structures have been found to exhibit size-dependent mechanical properties and ultra-high yield strength, due to a large fraction of surfaces. Also, these nanomaterials can possess a large number of microstructural interfaces, such as twin boundaries, which may influence their behavior at the nanoscale. The relationship between microstructure and plastic deformation in metal nanowire/nanopillar, however, has never been fully addressed.
The goal of this thesis is to investigate the effects of twin boundaries on the plastic deformation of gold nanowires by parallel molecular dynamics simulation. The simulations were carried out with an Embedded-Atom-Method interatomic potential and approximately 450,000 atoms. The model geometry consisted of a nanopillar of 122 Å, in diameter and 360 Å in length standing on a 35 Å - thick gold film. This model was investigated for loading conditions that could possibly be reproduced with an AFM, i.e. uniaxial compression, one fixed-end bending, and doubly-clamped bending. All calculations were performed to simulate the behavior of the pillar at 300 K using a Nose-Hoover thermostat for up to 10 ns.
The findings of this study are that twin boundaries act as obstacles for partial dislocations nucleated fiom the surface and result in strain hardening in gold nanowires under compression. Twin boundaries were also found to migrate by a mechanism of partial dislocation dissociation on twin boundaries, which resulted in strengthening. Doubly-clamped nanowires under bending were found to deform by twinning, which is different from the case of one fixed-end bending, where deformation occurred by slip only. The process of interface plasticity can provide a new insight into the process of deformation of gold at the nanoscale.
The goal of this thesis is to investigate the effects of twin boundaries on the plastic deformation of gold nanowires by parallel molecular dynamics simulation. The simulations were carried out with an Embedded-Atom-Method interatomic potential and approximately 450,000 atoms. The model geometry consisted of a nanopillar of 122 Å, in diameter and 360 Å in length standing on a 35 Å - thick gold film. This model was investigated for loading conditions that could possibly be reproduced with an AFM, i.e. uniaxial compression, one fixed-end bending, and doubly-clamped bending. All calculations were performed to simulate the behavior of the pillar at 300 K using a Nose-Hoover thermostat for up to 10 ns.
The findings of this study are that twin boundaries act as obstacles for partial dislocations nucleated fiom the surface and result in strain hardening in gold nanowires under compression. Twin boundaries were also found to migrate by a mechanism of partial dislocation dissociation on twin boundaries, which resulted in strengthening. Doubly-clamped nanowires under bending were found to deform by twinning, which is different from the case of one fixed-end bending, where deformation occurred by slip only. The process of interface plasticity can provide a new insight into the process of deformation of gold at the nanoscale.