Atomistic Simulation Studies Of The Mechanical Properties Of Metal-filled Carbon Nanotubes

Metal-filled carbon nanotube(CNT)composite structures have attracted much attentions in recent years due to their superior physico-mechanical properties and potential applications as active components in various nano-devices.As the foundational performance,the mechanical properties of the related materials not only determine the deformability and integrity of the structures,but also affect the functionalities of related nano-devices.Thus,understanding the formation mechanisms of metal-filled CNT composite structures and the structure-property relationships are of great importance for the preparation and evaluation of related nano-devices.In the present work,the crystallization behaviors and mechanical properties of CNT-polycrystalline/nano-twinned copper nanowire(CuNW)composite structures are studied.Firstly,based on the molecular dynamics(MD)simulation,the crystallization behaviors and mechanical properties of CNT encapsulated polycrystalline CuNWs are investigated.The influences of the wall number of CNT,the cross-sectional diameter and the cooling rate are considered.It is found that the CNT acts as a template to induce the nucleation of copper atoms from the surface and the template effect is mainly dominated by the innermost layer of CNT via the van der Waals interaction.CNT encapsulated CuNW can be formed after the cooling process and the internal CuNW is composed of several circumferential fan-shaped polycrystalline grains separated by the radial grain boundaries.The crystallinity increases with the increase of the diameter and the decrease of the cooling rate.Tensile tests show that the strength of the composite structure of the CNT encapsulated CuNW is much larger than the corresponding pristine CuNW.Moreover,it is found that the strength of the composite structure increases with the decrease of the diameter and the CNT plays a leading role in strengthening the materials.Secondly,the mechanical properties of CNT encapsulated twinned CuNWs are investigated based on MD simulations.Different cross-sectional diameters and twin spacings are considered.It is found that the CNT can significantly enhance the elastic modulus of twinned CuNWs,but will reduce the yield strain of the material.In the stage of plastic deformation,the plastic deformation of the composite structure is dominated by partial dislocation activities.CNTs and twin boundaries will greatly increase the flow stress of the material.The elastic modulus and ultimate strength of the composite structure have a strong size dependency.With the increase of the size of the composite structure,the elastic modulus and the yield strain of the composite structure decreases.The twin spacing has little effect on the elastic modulus and ultimate strength of the composite structure.The present findings will shed light on the fabrication and practical application of metal-CNT composite structures.