Study On High Efficiency Lapping Of Sapphire Wafer Based On Solid Phase Tribochemical Reaction

Sapphire??-Al₂ O₃?is widely used in the fields of national defense,industry and people's livelihood,owning to its excellent physical and chemical properties.For ultra-precision machining requirements of flat sapphire component and the characteristics of hard,brittle and hard machining of sapphire,the tribochemical mechanism of sapphire lapping with fixed abrasive tools based on solid phase tribochemical reaction is studied.Thermodynamic and kinetic analysis of solid phase reaction of sapphire are carried out.The mathematical model of tribochemical conversion rate is established.Fixed abrasive tools for tribochemical lapping sapphire are developed and the performance of the tools are tested.A series of experiments about sapphire lapped by the fixed abrasive tools are conducted on the improved lapping platform.The theoretical basis is provided for the selection of raw materials,the determination of manufacturing parameters about fixed abrasive tools and the lapping parameters of tribochemical lapping sapphire with fixed abrasive tools.And the practicability of this method is actively explored.The main research work and conclusions of this thesis are as follows:The primary problem of tribochemical lapping sapphire is the determination of materials that can react with sapphire.Whether the material has a tendency to react spontaneously with alumina is determined to preliminary exclude the materials without reaction trend,by calculating whether the gibbs free energy change of the possible chemical reaction between the primary material and alumina is less than zero.The Differential scanning calorimetry?DSC?analysis tests for mixtures of alumina and different materials that have a tendency to react with alumina are carried out.The materials with obvious reaction with alumina are screened by whether there are obvious endothermic trough or exothermic peak to keep narrowing down.The experimental data of DSC with obvious reaction with alumina are analyzed furtherly to calculate the reaction activation energy.The smaller the activation energy is,the easier it is to react with alumina.Based on the above analysis,Si O₂ is selected as raw material to lap sapphire within the scope of the primary materials of this study,and the activation energy can be further reduced by adding B₂O_3.Both mechanical and chemical action are strong and balanced,is the key to high removal rate and rapid improvement of surface quality during tribochemical lapping.According to the research by GREENWOOD about the contact between two rough surfaces can be simplified to an equivalent contact between a rough surface and a smooth plane,combining with the pure chemical general equation of solid phase reaction conversion rate,the mechanically strengthened solid-phase reaction conversion model for tribochemical lapping of sapphire with the fixed abrasive tools is established.The analysis of the model shows that the factors that affect the conversion rate mainly include the activation energy,the reaction temperature,pre-finger factor,surface convex peak density,convex peak radius of curvature,speed and load.The fixed abrasive tools are the carriers of the fixed abrasive tribochemical lapping sapphire.Raw material compositions are select based on chemical analysis.Abrasive particle size and percentage content are determined combined with conversion rate model.Then,the fixed abrasive tools are developed,the microstructure of which are observed and the properties arehardness and compressive strength are taken as the main evaluation indexes of the fixed abrasive tool.The lapping platform for small diameter fixed abrasive tools on the basis of drilling and milling machine is improved.The platform can meet the requirements of qualitative analysis and quantitative comparison of lapping effect,although there is still a gap between the ideal state and the practical application.A series of experiments are conducted on this platform.Five kinds of oxide abrasives tools are used to lap sapphire.Comparing the average removal amount per unit time and surface quality improvement,the hardness of the fixed abrasive tools with magnesium oxychloride as binder can meet the requirements of sapphire lapping,and the surface quality of sapphire after lappinging with Si O₂ abrasive tool is the best.The single factor experiments are carried out,and the qualitative trend of the experimental results is consistent with the conversion rate model analysis.Orthogonal test of factors affecting removal rate is done to determine the optimal combination of lapping parameters and manufacturing parameters of fixed abrasive tools are the rotating speed 150r/min,load 0.6MPa,Si O₂particle size 45?m,the mass fraction of Si O₂ 30%.Under the optimal combination condition,1 h mean value of removal height added with B₂O₃ is higher than the case without B₂O₃,the removal rate is effectively improved,and the nanometer surface quality is obtained.High efficiency and precision lapping of sapphire is realized and machining allowance and machining time for subsequent polishing process are reduced.