Investigation On The Deformation Mechanism Of Metallic Nanowires

To solve the innerstress problem in electrodeposited coating, we studied the deformation behaviors of transitional metallic nanowires (NWs) based on the self-developed ultra-large nanosimulation program. The effects of crystallographic orientation, defects, grain boundary, grain size, temperature and strain rate were considered to understand the elastic and palstic deformation behaviors of the metal NWs. Then, some mechanical properties and deformation mechanisms are obtanied and will list in below. It thus will be helpful to reveal the failure mechanisms of the nanosized materials under exteral loadings, and this could provide a insight into micro-nanofabrication technology.1. Anisotropic and temperature effects on mechanical properties of copper nanowires under tensile loading.Atomistic simulations are used to investigate the mechanical properties of copper nanowires along<100>,<110> and<111> crystallographic orientations under tensile loading at different temperatures. The inter-atomic interactions are represented by employing embedded-atom potential. To identify the defects evolution and deformation mechanism, a centrosymmetry parameter is defined and implemented in the self-developed program. The simulations show that Cu NWs in different crystallographic orientations behave differently in elongation deformations. The stress strain responses are followed by a particular discussion on yield mechanism of NWs from the standpoint of dislocation moving. Generally, the study on the incipient plastic deformation will be helpful to further understanding of the mechanical properties of nanomaterials. In addition, the Young’s modulus decreased linearly with the increase of temperature. The crystal structure is less stable at elevated temperatures.2. The mechanical behaviors of silver nanowires including point defects and3D defects.Molecular dynamics simulations are used to study the deformation of the silver NWs containing defects under tensile loading. The embedded atom method (EAM) potential is employed to describe the atomic interactions. The investigation designs various kinds of defects inside NWs and studies the influences of the defects on the strength, and dislocation emission, deformation mechanism. This work contains two parts, one part is the point defects effect on deformation behaviors of the NWs. we mainly focus on the elastic behavior of NWs at different loading rates and defect ratio. For the other part, The investigation designs ball-shaped closed cracks inside NWs. Analysis results demonstrate that if the leading dislocation are emitted from cracks, the strength of the defective NWs occur is lower than that of defect-free NWs. It also demonstrate that desigined NWs with different orientations behavior differently.3. The mechanical behaviors of twinned silver nanowires.The deformation of twinned silver NW is examined to reveal the strengthening mechanism of twinning boundary by using molecular dynamic simulation. In the first part, we study the mechanical responses of fivefold twinned silver NW for tensile and torsional deformations. Although the relaxed configuration of fivefold twinned NW possesses higher potential energy than<110> single crystalline NW, the internal stable of the unique structure provides a larger energetic barrier to defect formation. Under tensile loading condition, we find that the defect emission and propagation in fivefold twinned NW is prevented by the pre-existing twin boundaries. While the plastic deformation under torsion yield through the nucleation of coaxial dislocations, showing a quite uniformly distribution as observed in the end of the wire. In the other part, we study the mechanical responses of (111) twinned sliver NWs. Strong elastic deformation behavior and fast stress releasing are observed under tension loading. Analysis results also demonstrate that smaller twin boundary space could make greater improvement of elasticity of silver NWs.4. The mechanical behaviors of nanocrystalline and the single crytall nanowire under torsional loading.For the first part of this section, the construction of silver nanocrystalline (NC) samples by molecular dynamics simulation is investigated. Firstly, the initial NC samples are assembled by Voronoi geometrical construction method, then the local minimized energy states of the samples are obtained. The nanocrystalline grain structure is analyzed with radial distribution function (RDF), energy analysis and centrosymmetry parameter methods. Stress strain curves show the reverse Hall-Petch relation in the present simulations. The decrease of elastic modulus is dependent on the size of the nanostructure. In the second part, atomistic simulations are used to investigate the mechanical properties of<100> copper NWs under torsional loading. The loading rates, wire cross-sectional sizes and thermal effects on the critical angle of copper NWs are discussed. It may be predicted from our simulation that the NWs take different paths of deformation at different loading rates. For lower loading rates, the NW is showed clear periodic fluctuation characteristics in potential energy response, with dislocation and slippage occurring along the (111) plane. While in high loading rates, periodic fluctuation behavior become less clearly defined, and atoms cluster into disorder arrays near the two ends of the NW.