Mechanism And Process Research Of Lithium Niobate Lapping And Polishing By Fixed Abrasive Pad With A High Efficiency And Low Damage

Lithium niobate(LN)single crystal is one of the enduring materials and widely used in the infrared detector,laser,modulator,optical switch,multiplier and filter fields,owning to its excellent ferroelectric,piezoelectric and photoelectric properties.However,it has low hardness,great brittleness,and strong anisotropy,which lead to the wafers brittle failure,high subsurface damage,abrasives embedding and low efficiency during the traditional loose abrasive lapping and polishing processing.Based on this background,a new solution with hydrophilic fixed abrasive polishing technology(FAP)for single LN wafer was proposed.A series of researches were carried out on the mechanism of brittle-ductile transition of each orientation,the mechanism of workpiece/fixed-abrasive pad,the critical condition of abrasive embedment and the mechanism of abrasive pull-out,the formation mechanism and influences of subsurface damage and the process optimization of fixed abraisve lapping and polishing.In view of the low efficiency and pad wear problems in contimuous machining,a novel processing of abrasive aggregate was proposed for soft-brittle materials durable machining,that laid the groundwork for eccicient and low damage processing of LN wafer.The main contents of this thesis are as followings:1.Mechanism research of brittle-ductile transition of single LN wafers along each orientation.The Vickers hardness,fracture toughness and cracks formation of each orientation were invested on micro-hardness tester.The elastic modulus and the critical cutting depth were invested by nano-indentation and nano-scratching method,respectively.The effect of crystal structure on the brittle-ductile transition was analyzed and the formula of the critical cutting depth of each orientation was modified.The effect of slurry media on critical cutting depth was explored,and the effects of critical cutting depth on lapping material removal rate and surface quality were analysed.2.The mechanism research of abrasive fall-out,embedment and pull-out during lapping and polishing.The embedment abrasive was detected.The critical condition of sharp and spherical particles during loose abrasive was discussed.The abrasive fall-out and pull-out mechanisms during fixed abrasive were analyzed.3.The mechanism research and detection of subsurface damage based on fixed abrasive lapping.The improved angle polishing method was adopted to detect the subsurface damage depth during fixed abrasive lapping process.The effects of lapping method,lapping parameters and the hardness of fixed pad matrix on the subsurface damage depth were investigated.The formation mechanism ofsubsurface damage by fixed abrasive lapping was research.4.The cutting depth and surface roughness modeling.The interface bonding strength tests between abrasive and resin matrix were carried out.The main reason of abrasive fall-off was definite through the quantitative calculation of bonding force.The fixed abrasive “back-off” was analyzed and the cutting depth and surface roughness model of fixed abrasive lapping were built combined abrasive back-off and the bonding force.On this basis,the abrasive maximum height,cutting depth and surface roughness can be predicted with given process conditions.Meanwhile,the pull-out of the incident embedment abrasive was verified.5.The process optimization of fixed abrasive lapping and polishing.The self-developed lapping and polishing pads were adopted to explored the process of the single LN crystals.The orthogonal experiment was adopted to research the effects of the process parameters(applied load,table speed,and abrasive surface treatment)on the material removal rate and surface roughness of LN fixed abrasive lapping and polishing.The reasonable process route and optimum processing parameters were obtained.6.The novel aggregate abrasive for lithium niobate fixed-abrasive durable machining.The self-condition property of fixed abrasive pad was explored during lithium niobate lapping and polishing based on the matrix hardness and abrasive morphology.The aggregate abrasive was put forward to ensure the efficiency of durable machining of lithium niobate wafers.