Anisotropic Deformation Behavior Of AlN Ceramics And Its Application In Precision Grinding

Aluminum nitride(AlN)ceramics have the advantages with high resistivity,high heat conductivity,high dielectric constant and the thermal expansion coefficient similar to silicon,which is considered to be the ideal electronic packaging substrate,and has a very broad application prospects in insulated gate bipolar transistor(IGBT),5G communication radio frequency components,high power LED and other functional devices packaging.However,AlN ceramics are not only hard to remove due to its high hardness,but also easy to occur brittle remove due to its low fracture toughness,resulting in microcracks and other defects on the surface/subsurface;Moreover,AlN ceramics have random grain orientations and different mechanical properties,which makes it very difficult to obtain high integrity surface.Therefore,it is very important to understand the anisotropic mechanical properties,deformation behavior and removal characteristics of AlN ceramics at grain size for precision/ultra-precision machining of AlN plastic domain to obtain AlN ceramic substrates with high integrity.The Berkovich diamond indenter was used to perform indentation experiments at different indentation depths(200nm-1500nm)to analyze the anisotropic deformation behaviors of AlN ceramics,such as slip line,pile-up,residual depth and elastic recovery.Schmidt factor calculation model is established to determine the three typical crystal planes(0001),(101?0)and(1?21?0)are the most likely to be activated slip system;The subsurface dislocation distribution,uniaxial stress atomic distribution,subsurface atomic slip direction distribution during the indentation of three typical crystal surfaces were analyzed by molecular dynamics simulation,and the mechanism of activation anisotropy of slip system of typical oriented grains was revealed.The distribution of slip lines on the surface of grain with random orientation is analyzed theoretically by using indentation Schmidt factor calculation model and slip trace method,which is in good agreement with the actual slip line of the indentation surface.The relationship of AlN hardness,elastic modulus and elastic recovery rate with main Euler Angle is obtained by array indentation experiment in plastic domain.The relationship between the pile-up,residual depth,the depth of the dislocation and elastic recovery rate of the three typical crystal((0001),(101?0)and(1?21?0))and grain orientation is obtained by molecular dynamics simulation,and analyzes the mechanism of anisotropic.The scratched surface/subsurface morphology characteristics of AlN ceramics were observed and the anisotropy of deformation behavior was analyzed.A scratching Schmitt factor model was established to study the mechanism of anisotropic behavior of the slip line on the scratch surface of grains with different orientations.The evolution law of material friction characteristics under different scratch experimental conditions was investigated,and the influence of different scratch speeds and normal loads on the friction coefficient was analyzed.Through the molecular dynamics simulation of three typical crystal plane scratching processes,the relationships of the mechanical properties of the scratches,the surface pile-up and the distribution characteristics of subsurface dislocations with the crystal orientation were analyzed,and the causes of anisotropy were explained.The change law of the scratch residual depth and elastic recovery rate of grains with different orientations were studied,and the change curves of the residual depth and elastic recovery rate with the main Euler Angle of grains were obtained.The prediction model of AlN elastic recovery rate based on the mechanical properties of grains with different orientations and Schmidt factor was established.In order to study the generation mechanism and propagation law of indentation crack,indentation experiments were carried out under different indentation loading(0.1N-0.5N),and it was found that the starting point of the crack was not at the indentation tip,no matter it was ingrain crack or intergrain crack.The initiation of intrachrystalline cracks is caused by grain slip,and its direction is consistent with that of the most easily activated slip system.In order to obtain the fracture toughness of AlN,the high load(4.9N and 9.8N)indentation experiments were carried out.The basic mode of crack propagation under heavy load was understood.The effect of grain orientation on fracture toughness was obtained.And the macro fracture toughness of AlN was calculated based on the percentage of grain orientation distribution on the surface.According to the anisotropy of fracture toughness,the critical transition depth of AlN as a function of the main Euler Angle of grain was obtained.The resin bonded diamond grinding wheel was used to grinding AlN material.The surface characteristics of the grinding process were analyzed by means of SEM,EBSD and chemical corrosion,and the effects of anisotropic deformation characteristics of AlN on the grinding surface morphology and material removal were analyzed.Thus,the critical conditions of AlN material removal mode were obtained.The effects of grain size,linear speed,feed speed and grinding depth on surface quality during precision grinding were studied to obtain the optimal process parameters for plastic domain grinding.