Research On Nanoindentation/Nanoscratch Of Single Crystal SiC

As the third generation of semiconductor materials,single crystal SiC crystal has been widely used in precision components due to its excellent properties of high thermal conductivity,hardness,high temperature resistance,strong stability and radiation resistance.Because single crystal SiC is a typical hard and brittle material,surface/subsurface damage such as brittle fracture and cracks is easy to occur during its processing,which seriously affects the service performance and life of components.Based on this,in order to obtain nanoscale surface finish and non-damaged subsurface,on the basis of numerical simulation,this paper carried out a single crystal SiC nanoindentation/scratch experimental study to explore its nanomechanical properties and nanoindentation,Material removal and crack propagation mechanisms during scratching.The main contents of the paper are as follows:(1)The numerical simulation of single crystal SiC nanoindentation and scratching process was carried out,and the effects of indenter type,indenter tip curvature radius and machining depth on the material removal process were explored.The results show that with the increase of the indentation depth,the material is transformed from plastic deformation to brittleness and removed,and transverse cracks and median cracks appear on the subsurface of the material.Under the same indentation parameters,the brittle fracture damage caused by the Vickers indenter is the smallest,while the Berkovich indenter is the largest;with the increase of the scratch depth,the brittle damage and strain energy of the material will increase;When the radius is smaller than the machining depth,the influence of the radius of curvature on the scratching process is small.(2)The nanomechanical properties of 4H-SiC and 6H-SiC single crystal SiC materials were studied by nanoindentation test.The results show that the average elastic modulus of 4H-SiC(silicon surface)and 6H-SiC(silicon surface)are about 730.1 GPa and 592.9 GPa,respectively,and the average nanohardness is about 53.4 GPa and 55.1 GPa,respectively;and the two materials Both showed obvious size effect;the elastic recovery rate of 6H-SiC was greater than that of 4H-SiC;the load-displacement curve analysis showed that the plastic deformation characteristics of 4H-SiC were better.(3)Through nanometer single and double scratching experiments,the material removal characteristics and crack propagation laws during the scratching process of single crystal SiC are analyzed.The results show that:with the increase of scratching depth,the subsurface has median cracks,transverse cracks and surface radial cracks successively.The result verifies the simulation model;the critical value of brittle-plastic transition of 6H-SiC(silicon surface)material is that the plastic removal area is larger than 4H-SiC(silicon surface),and the silicon surface is better than the carbon surface;the indenter edge is scratched forward The plastic removal area of the material is the longest and the quality of the scratched surface is the best.The indenter faces the front and the scratched way is the worst.The magnitude of the loading rate has little effect on the scratched depth,but the critical depth of brittle-plastic transition increases with the increase of the loading rate.Larger and smaller;material removal is achieved through two forms of crack interaction in the double-scratch process,namely the interaction of subsurface transverse cracks of double scratches and the interaction of subsurface transverse cracks and radial cracks.The interaction between them exacerbates the brittle fracture damage and removal of the material.