Study On The Mechanism Of Axial Ultrasonic Vibration-assisted Scratching Of Single Crystal Silicon Carbide Based On Molecular Dynamics Simulation

As a third-generation semiconductor materials,single crystal silicon carbide(Si C)has excellent physical and chemical properties and has become the main material for high-power device chip substrates,which are widely used in emerging fields such as aerospace,new energy,and so on.As a chip substrate,its surface needs to achieve damage-free surface requirements.The high hardness and brittleness of Si C make it challenging to achieve efficient and precise machining.Grinding is the main method to achieve high efficiency and precision flattening of Si C substrates,but the conflict between grinding efficiency and quality is still prominent.Ultrasonic vibration-assisted grinding(UVG)can improve both machining efficiency and machining quality,which can alleviate this contradiction to a certain extent.However,the lack of research on the mechanism has limited its advantages and restricted the wide application of this technology in the Si C substrate preparation industry.Based on this,this project proposes to investigate the mechanism of ultrasonic vibration-assisted scratching(UVS)of Si C.The molecular dynamics method(MD)is used to simulate the UVS process of single-grain and double-grain,and to establish the scratch force model of the UVS process to reveal the interaction mechanism between abrasive grain and workpiece and the interference mechanism between abrasive grains in the UVS process from the perspectives of scratching force,stress and amorphous layer.Based on the scratching process of a single abrasive grain,the scratching force model of UVS process of a single abrasive grain is also established.Finally,considering the coupling effect between parameters,an optimization idea is proposed to optimize the UVG process.The main research contents and conclusions include the following:(1)For the scratching process of single abrasive grain,the scratching force model of UVS was established according to the chip deformation,friction and material accumulation in the scratching process.The results show that the scratching force fluctuated periodically with the motion of the abrasive grain during the UVS process.The fluctuation periods of the tangential and normal forces are half of the vibration period of the abrasive grains,while the fluctuation periods of the lateral force is consistent with the vibration period of the abrasive grains.The theoretical calculation results and the simulation results of MD are in good agreement,which verifies the accuracy of the scratching force model of UVS.(2)The mechanism of the interaction between the abrasive grain and the workpiece during the UVS of a single abrasive grain was studied by MD simulations.It is found that the tangential and normal forces decreased,while the lateral force increases,the area of the stress concentration region,the thickness of the amorphous layer decreases,and the volume of the processed area increases.The effects of different parameters on the UVS process were also investigated.Compared with changing the scratching speed and depth,increasing the frequency and amplitude is more beneficial to improve the processing quality of UVS.The effect of UVS on different crystalline Si C can be obtained by reducing the tangential and normal forces,reducing the amorphous layer thickness and increasing the machining volume.(3)MD simulations were carried out to study the interference between two abrasive grains in the UVS process of Si C.The trends of the scratching force and amorphous layer with different abrasive grains spacing can be found that the critical spacing for the disappearance of intergranular coupling during UVS is significantly larger than that of conventional scratching,and the interference between the grains is significantly enhanced by the applied vibration.The overlap ratio is also used to quantify the interference between the abrasive grains.The increase of the overlap ratio,the stronger the interfering effect between abrasive grains,and the greater the reduction ratios of tangential force and normal force.(4)An optimization idea is proposed to optimize the UVG process using only three parameters(vibration angle,contact area and influence coefficient between adjacent abrasive grains)based on the trajectory of abrasive grains,the mutual contact relationship between workpiece and abrasive grains,and the geometric parameters of abrasive grains.The relationship between these three parameters and the scratching force was established by MD simulations.And the correlation analysis showed that the vibration angle had the greatest influence on the reduction ratio of the scratching force in the UVS process.Finally,the UVG experiments verified that the optimization idea could be used for the optimization of UVG process parameters.The research content of this paper provides a theoretical basis for the use of ultrasonic vibration-assisted grinding technology for efficient and precise machining of Si C substrates,and provides theoretical guidance for process optimization and tool preparation for ultrasonic vibration-assisted grinding processing.