Simulation Study On The Mechanical Properties And Tensile Deformation Mechanism Of Gold Nanowire

Gold nanowires as an one-dimensional nanomaterials usually has excellent biocompatibility, chemical stability and high electric conductivity, which had opened up useful applications in the biomedical and nanoelectromechanical fields. In this dissertation,molecular dynamics method was used to study the tensile mechanical behavior and microdeformation mechanism of single gold nano wires and [111]-oriented gold nano wires containing different densities of parallel twin boundaries.The main conclusions are as follows:(1)The effect of diameter on the Young's modulus in single gold nano wires was not obvious,while the effect of crystallographic orientation is obvious.The Young's modulus of nanowires with different crystallographic orientations are shown as E[111]>E,[110]>E[100] .The yield stress of [100] nanowire is much higher than that of [110] and [111] nanowires, and the former one reach more than 2 times of the latter ones.The effect of strain rate on the mechanical properties such as elastic modulus, yield strength and fracture strain of gold nanowires under low and medium tensile strain rates is very weak, but these mechanical properties increase rapidly at high strain rate regions.The effect of twin boundary spacing on the yield stress in gold nanowire is obvious.With increasing twin boundary spacing , the yield stress of nanowire is decreasing.When the twin spacing reaches a certain value, the yield stress changes slightly.(2)The different distinct types of mechanical behaviors and micro-deformation mechanism were displayed in single [100]-oriented gold nano wires at the different strain rates.At the low strain rate(??1.0×109s-1), the stress-strain curve displays periodic zigzag increase-decrease feature, and the plastic deformation is resulted from the slide of dislocation,dislocations generated, expanded and escaped at each yield stage.At the medium strain rate(1.0×109s-1<??1.0×1010s-1), the stress-strain curve gently decreases during the plastic process, and the deformation is contributed from slid and twinning,dislocations can not fully extend and escape in the yield process, instead cross each other and reside within the nanowire.At the high strain rate(?>1.0x1010s-1), the stress-strain curve wavelike changes during the plastic process, and the deformation is resulted from the amorphization. The deformation processes of Au nanowire at the low,medium and high strain rates are investigated by the evolution of differernt microstructural configurations,the system is rapidly transformed into a disorderly amorphous state in the yield process, and the fracture strain is as high as 435.89%, showing superplasticity.(3) The deformation of Au nano wires with different crystallographic orientations are all caused by slip. [100]-oriented nanowire has four slip planes during the plastic deformation process, but only one plays a major role in the plastic deformation. The distance of stack faults increases during the plastic deformation process of [110]-oriented nanowire.With the change of the slip directions, the blockage of the nanometer block causes the final breakage of the nano wire..(4) Twin boundary spacing has a great influence on the yield stress of gold nano wires.WhenTBS is less than 2nm,the work together of dislocation and twin boundarie enhances the spaces of twin boundary in the necking region of nanowire, and then the twin boundaries block the slipping and change the slip direction.Thus the nanowires are strengthened.When TBS is greater than 2nm, the nano wires are softened.(5)The soften mechanisms can be divided into two types according to the distance of twin boundaries. When2nm<TBS<5nnm, the twin boundaries do not effectively prevent the slip of dislocations.With the dislocations accumulate, the dislocations break the restrict of the twin boundaries, and then some new dislocations are generated in the adjacent twinning regions,accompanying with the disappear of some incomplete dislocations.The nanowires fail to form stress concentration, and the strain strain is relatively large.WhenTBS>5nm,the dislocation slip causes the nanowire twin boundaries to be destroyed and then form a shear band.The disordered atoms accumulate in the twin plane, making the nanowire fracture strain smaller.