Simulation And Experimental Study On Ultrasonic-Electro-Chemical Mechanical Polishing Of Monocrystalline Silicon Carbide

Silicon carbide material has many excellent properties,such as high strength,high hardness,high density as well as excellent high temperature resistance,wear resistance,small thermal expansion coefficient,good impact resistance,etc.,making it a broad application prospect in aviation,aerospace and communications.However,the extremely strong chemical inertness and high hardness of SiC materials make it difficult to achieve a high level of material removal rate and an atomically flat surface simultaneously by current machining methods.This paper focuses on the ultra-precision machining of SiC materials.It involves theoretical and experimental studies on the compound polishing with electrochemical assistance,ultrasonic vibration and semi-fixed abrasive polishing to improve surface quality and processing efficiency of SiC materials.Using COMSOL Multiphysics software,the flow field modeling and simulation analysis of the slurry area between the test piece and the polishing plate were conducted,and the effects of different ultrasonic frequencies,amplitudes and polishing pads on the pressure and velocity of the flow field were investigated.The simulation results show that both the velocity and the pressure of the fluid increase as the ultrasonic frequency or amplitude increases.When using the multi-hole polishing pad,the fluid velocity under the test piece becomes smaller and more stable,the pressure increases nearly one hundred times,and the cavitation becomes stronger,which is more conducive to the generation of chemical reaction radicals.Using COMSOL Multiphysics Software,the temperature field,electric field and mass transfer process in polishing process of silicon carbide specimen were simulated and analyzed.The simulation results show that the temperature of the contact surface between the test piece and the polishing plate rises sharply at first,then gradually decreases,and tends to be gentle finally.With the increase of ultrasonic frequency and amplitude,the temperature rise of the sample surface also increases.When the multi-hole polishing pad is used,the voltage at the bottom surface of the test piece significantly increases,and the current density at the liquid hole of the multi-hole polishing pad is significantly higher than that at the surrounding solution.When the test piece is in contact with hydroxyl ions in Fenton solution,the corrosion rates at both edges are significantly higher than that at the bottom.An ultrasonic-electrochemical mechanical polishing experiment was performed on the silicon carbide specimens,polished by cast iron polishing plate,polyurethane polishing plate,semi-fixed abrasive polishing plate in three kinds of polishing liquids,i.e.tap water,KOH solution and Fenton reaction solution respectively,The material removal rate was calculated by the weighing method.The results show that the material removal rate is high when using cast iron polishing piate,but the surface quality is poor.The surface quality is best when using semi-fixed abrasive polishing plate,but the material removal rate is low.The Fenton solution has the best effect onimproving the material removal rate of the test piece.When the voltage between the test piece and the polishing plate is +10V,the material removal rate of the sample is the highest.The effect of ultrasonic vibration on the polishing of silicon carbide specimens is greater than that of the electric field.It can be seen that ultrasonic vibration plays a major role in the polishing of silicon carbide specimens.