Research On Deformation Mechanism Of Single Crystal Silicon Carbide Based On Molecular Dynamics Nanoindentation Simulation

As a third-generation semiconductor material,silicon carbide(SiC)has attracted wide attention for its excellent properties,such as wide bandgap,high thermal conductivity,and high breakdown electric field strength.However,SiC is one kind of super hard material and is difficult for processing.It is difficult to avoid the damage on surface and sub-surface during processing.The deformation behavior and damage mechanism are still unclear,which also severely restricts the design,manufacturing and application of SiC.Therefore,the research on the mechanical properties of SiC has always been a hotspot in the international academic community.In recent years,nanoindentation testing technology has gradually become the mainstream testing method for the micromechanical properties of materials.Research on nano-indentation of SiC has been gradually carried out by scholars domestically and abroad,and some research achievements on deformation behavior and mechanism of single crystal SiC have appeared.However,the nanoindentation test has its own limitations.In the process of nanoindentation,the deformation behavior of the surface and subsurface for tested material is difficult to be monitored dynamically in real time,which also limits the development of nanoindentation technology.In order to study and elucidate the micro-mechanical properties and mechanical mechanism of SiC,combining with research and analysis in related fields in China and abroad,this paper proposes a molecular dynamics-based nanoindentation simulation method in response to the above problems.This dissertation studies and discusses the mechanical properties,elastic and plastic deformation,the initiation and evolution of phase transitions,and the anisotropy of 4H-SiC and 3C-SiC materials.Considering the high hardness of SiC,the diamond indenter will deform during the indentation process.This article studies the influence of the deformation of the diamond indenter on SiC and revises the nanoindentation test results of SiC.The main content of the paper is as follows:(1)The molecular dynamics model of single crystal silicon carbide material has been established.Aiming at the structure of SiC,a molecular dynamics simulation model of single crystal3C-SiC and 4H-SiC material nanoindentation is established;based on the experimental results,the Vashishta potential is applied to describe the internal atomic interaction of SiC.The ABOP potential describes the interaction between the diamond indenter and the silicon carbide material atoms.The method for solving the equation of motion,the ensemble of the system and the boundary conditions is selected.The article also describes the principles of molecular dynamics,silicon carbide crystal structure and defect analysis methods,and the modeling of nanoindentation for SiC.The article also describes the basic principles of molecular dynamics,silicon carbide crystal structure and defect analysis methods,and the modeling process of silicon carbide nanoindentation.(2)The deformation and damage mechanism and the anisotropy of the 3C-SiC material during the nanoindentation process were studied.Molecular dynamics method is selected to simulate the nanoindentation process of the spherical indenter on 3C-SiC(010),(110)and(111).At the same time,the deformation behavior and damage mechanism of 3C-SiC is studied,and the anisotropy of 3C-SiC is analized.The research results show that the plastic deformation of 3C-SiC is caused by the nucleation and expansion of the dislocations which triggers a large number of directional movement of atoms.This phenomenon is indicated in pop-in on the load-indentation depth curve.The dislocation is generated at the bottom of the elastic deformation zone and gradually expands to form V-shaped dislocation loops and prismatic dislocation loops.The prismatic dislocations extend inwards the specimen along the<110>orientation.The article uses Thompson tetrahedron to explore the changes of material structure indentation on different crystal planes during nanoindentation of 3C-SiC,and finds that the anisotropy shown by 3C-SiC can be explained by different angles of the indented surface and Thompson tetrahedron.(3)The deformation and damage mechanism and the anisotropy of the 4H-SiC material during the nanoindentation process were studied.Molecular dynamics method is selected to simulate the nanoindentation process of the spherical indenter on 4H-SiC(0001)crystal plane.The elastic and plastic deformation behavior of 4H-SiC is studied.The deformation behavior and mechanical mechanisms of phase transition in 4H-SiC nanoindentation is also studied layer by layer.The study indecates that in the process of 4H-SiC indentation,perfect dislocations are likely to result in plastic deformation,and a small amount of imperfect dislocations were found.The cube corner indenter is rotated around axial direction for the studying of anisotropy of 4H-SiC:When the edge of the indenter is parallel to the[~—1010]crystal orientation,a phase transition from4H-SiC to 3C-SiC occurs inside the material.This phenomenon is mainly caused by the expansion of shear stress and incomplete dislocations.The article also conducts nanoindentation experimental research on 4H-SiC,which is mutually confirmed with the theoretical research results.(4)The influence of the diamond indenter deformation during the indentation of SiC is studied,and a method to correct the indenter deformation is put forward.For the deformation behavior of the diamond indenter in the process of silicon carbide nanoindentation,molecular dynamics simulation methods were used to simulate the deformation behavior of spherical indenter,cube corner indenter and quadrangular pyramid indenter during nanoindentation of 3C-SiC material.The deformation mechanism of different indenters during indentation is discussed,and the influence of indenter deformation on the deformation behavior of 3C-SiC material is studied as well as the results of indentation testing.Aiming at the deviation caused by the deformation of the diamond indenter,a theory is put forward for three kinds of diamond indenter on correcting the load-displacement curve from nanoindentation.The hardness-displacement curve of the indentation is also corrected.The study of this problem fills the gap in the influence of indenter deformation on material deformation behavior.This study is is of great significance for the understanding of the deformation behavior and mechanical mechanism of SiC as well as the influence of deformation of the indenter.It also provides important theoretical support for the design,manufacturing and application of SiC.