Effects Of Defect Structure On The Properties Of Silicon Carbide Nanowire

Silicon carbide(SiC)nanowires are widely used in electronic devices in extremely harsh environments because of their excellent properties such as high temperature and pressure resistance,high mechanical strength,and radiation resistance.Currently,refractory materials melt at high temperatures and very little is known experimentally about the melting mechanism of SiC nanowires.Mechanical performance is one of the key considerations for material use,however,brittleness at room temperature and dispersion of mechanical properties limit the further use of SiC nanowires.The microstructure of a material determines its macroscopic properties.In this paper,from the perspective of defective structure,the structural response of defective SiC nanowires containing vacant atoms,interstitial atoms,twin boundaries,stacking defects,polycrystalline boundaries,mixed crystals,and intergranular amorphous layers under melting and tensile and compressive loading has been investigated by means of molecular dynamics simulations.The main contents are as follows.First,the melting behaviors of the above seven types of defective structures and single-crystal SiC nanowires were simulated based on molecular dynamics.Overheating of SiC nanowires due to high-temperature rise rate.It was found that the defects have little effect on the melting point,but strongly influence the melting behavior of the nanowires.The melting of SiC nanowires can be divided into three stages: structural stabilization,pre-melting of surface atoms and accelerated melting after reaching the melting point.If a high-energy grain boundary is preset,the melting will extend along the grain boundary to the interior,if not,the nanowire will deform and completely melt back to its original state.During the melting of single-crystal SiC nanowires,the melting order of atoms is Cubic diamond(2st neighbor)→ Cubic diamond(1st neighbor)→ Cubic diamond → Other atoms.Then,the effects of different defect structures and defect concentrations on the mechanical properties of SiC nanowires under tensile and compressive loading were systematically investigated,respectively.The mechanical properties of SiC nanowires under tensile and compressive loading decrease with the increasing concentration of vacant and interstitial atoms.The twin boundaries and stacking defects show asymmetry in tension and compression,and these two types of defects tend to become fracture sites in tension,but the opposite is true in compression,where the extension of these two types of defects is hindered under compressive strain.A large number of shear bands at 19.47° to the [111] axial direction were found in the stacking defects.The mechanical properties of polycrystalline SiC nanowires are independent of the number of grains and are related to the type of grain boundaries.Mixed crystalline forms and intergranular amorphous layers possess plastic characteristics.The mixed crystalline forms first slip out of the interface under tensile and compressive loading,and the fracture of old Si-C bonds and the creation of new Si-C bonds are the cause of plasticity.The self-healing process of recrystallization of the intergranular amorphous layers was found under tensile loading,while this phenomenon was not found under compressive loading due to the impeded movement of the amorphous layer atoms.Therefore,the experimentally measured mechanical property dispersion is not only related to the defect type of the SiC nanowires but also influenced by the test method.To enhance the plasticity of SiC nanowires and even semiconductor materials when the grown SiC nanowires are in the [111] direction,sliding through the atomic layers at 19.47° to the axial direction may be an effective method.