Study On Cutting Mechanism Of SiC Monocrystal Based On Scratching Experiment

SiC monocrystal with good material properties has been widely used in various engineering applications,including in the aerospace,high power devices.However,it is well known as a difficult-to-machine material because of its high hardness and brittle nature.In recent years,some studies on material remove behaviors of glass and silicon were reported which confirmed that it was possible to ductile-machining hard and brittle materials with the certain cutting conditions.This studies provided a theoretical support for the realization of ductile regime machining SiC single crystal materials.Based on the theory of plastic flow and the theory of indentation plasticity,the mechanism of plastic deformation under indentation was analyzed.The scratch model was established and the relationship between load/depth was obtained.The critical depth of SiC monocrystal,at which ductile to brittle transition in deformation occurs with vibration-assisted machining,can be required by analysising material remove energy model during the cutting process.The theoretical model of the scratching load and depth of the three-sided pyramidal probe is established.The depth of scratches can be calculated by the load applied to the probe and material yield strength.Deformation and remove characteristic in nanoscratching 4H-SiC monocrystal wafer with using AFM by linearly increasing tip force has been studied.Material ductile deformation remove occurs during the process that the tip force was varied from 0 μN to～150 μN linearly across the length of the line.linear relationship of groove depth and tip force has been found.After repetitively nanoscratching 4H-SiC monocrystal wafer with the same conditions,materials next to the end of groove was removed by brittle fracture.The depth of the groove was linearly increased during the scratches,and the depth of the groove was linear with the normal force applied to the probe tip.Aiming at researching the critical cutting depth of the hard and brittle materials during the micro-nano cutting process,a set of micro-nano-scratching system had been designed.The scratch experiments were carried out under conventional conditions and ultrasonic vibration assisted conditions by four single point diamond tools with different tool angle and tool nose radius under the micro-nano-scratching experiment system and Leica DCM3D.According to the change of cutting normal force and groove surface morphology,material remove behavior and the effect of tool angle,tool nose radius and ultrasonic vibration on the critical depth of 4H-SiC single crystal were analyzed.When the angle of diamond tool is the same,the critical cutting depth of 4H-SiC single crystal increases with the radius of the tool nose radius.When the radius of tool nose radius is the same,the critical cutting depth on ductile-brittle transition of 4H-SiC single crystal increases with the increase of the tool angle.Under the same scratch conditions,the ultrasonic vibration-assisted scratching is better than the conventional scratching to improve the groove surface morphology of 4H-SiC single crystal,increase the critical cutting depth,reduce the cutting normal force.