Molecular Dynamics Simulation Of Tension Of Body-centered Cubic Tungsten Single Crystal Nanowires

Single crystal nanowires are an important basic component of micro-nano electromechanical systems(MEMS / NEMS).Body-centered cubic metal tungsten has the advantages of corrosion resistance and good heat insulation.It is an ideal material for single crystal nanowires.Therefore,in order to better apply tungsten single crystal nanowires(STNW)to micro-nano electromechanical systems,we urgently need to study the mechanical behavior of STNW.In this thesis,large-scale molecular dynamics simulations were used to conduct a series of tensile test studies on STNW.The crystal orientation dependence of its mechanical behavior was studied from the perspective of crystal orientation,and the environmental temperature,nanowire cross-sectional shape,size,and loading rate were studied.The effect of different crystal orientations on the mechanical behavior of STNW was also investigated.The effect of doping carbon atoms on the mechanical properties of STNW was also investigated.The stress-strain curves of STNW simulated under different conditions were obtained.The deformation behavior of the STNW was analyzed in conjunction with the atomic visualization images of the stretching process.The STNW tensile deformation was explored by means of local crystal orientation recognition,dislocation recognition,and centrosymmetric parameter analysis mechanism.From the research results,we found:(1)STNW's deforming machine is determined by the crystal orientation.Environmental temperature,nanowire cross-sectional shape,size,loading rate(high strain rate range)cannot change the STNW's deformation mechanism.STNW is in [001] crystal orientation and adjacent crystal orientation [013],[113] exhibits plastic twin deformation,twin system {112} / <111>,elongation is up to more than 50%;STNW is in [111] crystal orientation and adjacent The crystal orientations [011],[133],[223],[233] exhibit brittle fracture,and the fracture strength limit is nearly double that of the plastic crystal orientation.The [111] crystal orientation STNW cleavage plane is {110}.Dislocation slip is notobserved in most stages of STNW tensile deformation.(2)Whether it is twinning or crack initiation,it nucleates on the surface of STNW and nucleates on the outer surface of single-crystal tungsten nanotubes.The twin-boundary crystal plane index is {112}.The extension direction is determined jointly and is not fixed.(3)All crystal orientations show a certain degree of strength(yield strength and fracture strength)in a linear decreasing relationship with the square root of temperature;the strength of the square section STNW is higher than that of the circular section,and the strength of the hollow section is equivalent to the solid section;the critical point of size effect Located between 2.53 ? 3.17nm(8 ? 10 lattice spacing);the change of loading rate does not change the intensity.(4)The addition of impurity C atoms greatly reduces the strength of STNW and slightly improves the plasticity of STNW.Both twin embryos and crack initiation are transferred from the STNW surface to the C atom.