| As a high-performance material,silicon carbide(SiC)possesses superior mechanical and electronic properties,including high corrosion resistance and high oxidation resistance as well as high saturated electron mobility.Therefore,it has found extensive application in semiconductor chips,microelectromechanical devices(MEMS),and optical sensing elements.However,due to the low surface energy and large Young’s modulus of SiC material,it is highly brittle and hard with low fracture strength,leading to the formation of cracks,voids,and vacancies in the workpiece,which exacerbates surface quality and surface integrity of the workpiece.To improve the machinability of SiC material,this thesis proposes a new processing method that combines surface texture and water lubrication to reduce friction and wear by altering contact characteristics between the abrasive and the workpiece,while minimizing temperature influence.Additionally,molecular dynamics(MD)simulation is applied as an economic and effective tool to analyze the nano-indentation process and grinding process of single-crystal cubic SiC machined by a diamond abrasive in water lubrication,revealing many physical behavior mechanisms that occur continuously at the atomic scale.The main research contents and conclusions of this thesis are as follows:(1)To unveil the effect of water film on the physical behavior mechanism of SiC material,a nano-indentation simulation of single-crystal cubic SiC was carried out using MD tools to investigate the effect of water film thickness on the physical behavior mechanism.The study examined the effect of water film thickness on the lattice structure deformation,load vs.depth curve,stress,dislocation,sub-surface damage,and surface morphology were analyzed during nano-indentation.The simulation results revealed that the depth of a pop-in event occurrence of the substrate with water film is reduced,which enhances the plasticity of SiC material.Additionally,the water film can change the behavior characteristics of dislocations in the substrate,improve the bulge atom distribution on the substrate surface,and reduce the adhesion of amorphous atoms to the diamond indenter.(2)MD simulations were conducted on the grinding process of single-crystal cubic SiC textured surface in water lubrication to investigate the influence of water film thickness on the friction performance and material removal behavior of SiC.During grinding,the temperature,grinding force,friction coefficient,stress,tool wear,dislocation,and surface topography were analyzed by comparing different water film thicknesses.Moreover,a Rayleigh chip thickness model was employed to predict changes in workpiece surface roughness.The simulation results indicated that the friction behavior and machining performance of textured workpieces are improved,with the machining performance of the workpiece in water lubrication being further enhanced.The theoretical model predicted that the surface roughness of the workpiece in water lubrication is improved.(3)MD tools were applied to simulate the grinding process of single-crystal cubic SiC textured surface in water lubrication.The effects of grinding depth and grinding velocity on the physical behavior of SiC were studied.The study analyzed the temperature,grinding force,friction coefficient,stress,dislocation,and surface topography by comparing different grinding parameters.Additionally,the Rayleigh chip thickness prediction model was employed to study the influences of grinding speed and grinding depth on workpiece surface roughness.The simulation results stated that increasing the grinding depth will strengthen the material removal rate,but it aggravates the sub-surface damage of the workpiece and reduces the machining quality.High-speed grinding can enhance the machinability of SiC,and more heat will be generated.The theoretical model predicted that a large grinding depth will increase the surface roughness,while the surface roughness of high-speed grinding will be improved. |
