Study On Brittle-ductle Transition Mechanism Of SiC Monocrystal And Experimental

The SiC monocrysta,only second to diamond in hardness,is a typical hard and brittle material.It has been widely used in high power devices and IC industry due to its good physical and mechanical properties.However,the processing process of SiC monocrystal wafers becomes very difficult for its high hardness and brittlene.ss.The proposition of ductile regime machining is an effective way to improve the surface quality of hard brittle m aterials,lots of research has been conducted on ductile-brittle transition of glass,quartz and silicon.It provides.a theoretical support for the precise machining and material removal mechanism of hard-brittle m aterials.This thesis study on SiC monocrystal material removal mechanism based on acoustic emission by usin g the diamond tool to scratch the surface of SiC monocrystal to study th e existence of ductile regime machining as well as the observation of the SiC mon ocrystal grooves surface and chip morphology.According to the exp eriment,SiC monocrystal also has a critical condition of ductile-brittle transition like other typical hard and brittle materials.When the cutting depth is less than the critical depth of cut,the SiC monocrystal is removed in plastic way,whereas removed in brittle manner,and the relationship between acoustic emission Kaiser effect point and brittle-ductile transition has also been studied,the result shows that the acoustic emission increase significantly when loaded to a certain condition,the acoustic emission frequency plays an significant important on material removal status.In order to acquire more accurate critical condition associating with tool angle and tip radius,the 90° and 1200,with tip radius of 50 ?m,100 ?m and 150 ?m respectively,are applied to conduct scratching test,the Leica DCM3D and SEM are used to research the scratching grooves to understand the critical depth of cut and the relationship between frictional force and brittle ductile transition is also studied.The result sho,ws that the critical depth of cut for 90° and 120°,with tip radius of 50?m,100 ?m and 150 ?m respectively,are 134nm,232.56 um,398nm,242nm,643,9nm and 788nm respectively.So when the tool angle is set,the critical depth of cut increases with the increasing the tip radius,when the tip radius is fixed,the critical depth of cut increases with the increasing the tool angle in a certain range.The loading force and the frictional force from the linear into fluctuation also present the brittle-ductile transition.