Research On Mechanical Properties And Deformation Mechanism Of Polycrystalline Copper Nanoindentation

In recent years,the wide application of Nano-materials in aerospace,microelectronics and medical treatment has promoted the rapid development of Nanofabrication.The technology of Nanofabrication has become an important symbol of the development level of national science and technology.However,current research about Nanofabrication is still at the theoretical level which limit the development and application of Nanofabrication.As a new Nano-material,Nano-polycrystalline copper has excellent properties such as high resistivity,high strength and low thermal conductivity,and is widely used in the preparation of optoelectronic devices and other products.Based on molecular dynamics technology,this thesis studied the mechanical properties and deformation mechanism at ratio of alloying elements,nanoindentation simulations and grain size characteristics,by building nanoscale metal model and simulating material deformation in machining.The nanocrystalline copper(Cu-Pb)MD simulation model is generated using Poisson-Voronoi tessellation and inverse Monte Carlo method in this work,then the atomic internal stress,and plastic deformation mechanism are revealed during the tensile process.The novel results can be summarized: With the increase of atomic component of Pb in the Cu-Pb alloy samples,the inhomogeneous distribution of the atomic internal stress at different locations of the microstructural compone nts can be effectively weakened.With the increase of the atomic fraction of Pb,the steep von Mises stress gradient in the grain boundary interface regions decreases continuously;meanwhile,the hydrostatic pressure gradient increases slightly.The lower von Mises stress gradient induced by the Pb component as a major factor can effectively delay the defect nucleation process in the alloy sample.The higher hydrostatic pressure gradient as a secondary factor is associated with the defect nucleation,which can promote the dislocation nucleation process.In this chapter,the nanoindentation simulations of polycrystalline copper with initial indentation positions at microstructural components were implemented using MD method.The defect evolution process and indentation-induced deformation mechanism were revealed and the novel results can be summarized: The indenter atoms interact with the workpiece atoms strongly,leading to the normal indentation force increasing rapidly during the indentation process.The defect distribution range of the workpiece is associated with the initial nanoindentation position.The defects nucleate in the indentation region and propagate to the microstructural components of the interfaces in the order of VP,TJ and GB,and then are absorbed by the interfaces.In this chapter,MD methods are used to investigate the grain size effects on plastic deformation mechanism and defect evolution of polycrystalline copper.The novel results can be summarized: The indentation-induced plastic deformation and defect evolution process are closely related to the structure of grain boundary interface,which is determined by grain size of polycrystalline materials.The indentation force of polycrystalline copper is lower than that of single-crystalline copper due to grain boundary network,and with the decrease of grain size in polycrystalline copper,the indentation force continuously decreases due to softening phenomenon.When the grain size comply with the inverse Hall-Petch relation,a smaller range of internal stress and defect distribution in the sample can be obtained during nanoindentation process,but the ductility of polycrystalline materials is also reduced.