Research On Fixed Abrasive Polishing Of LBO Crystal Using Non-Water Based Slurry

LBO(LiB3O5, Lithium Triborate) crystal plays a key role and has widely application in multiple fields, e.g. solid-state laser, inertial confinement fusion and laser display etc., with its excellent nonlinear optical properties. However, the processing of LBO crystal is difficult because of its softness, brittleness and micro-deliquescence. The surface quality of LBO crystal is directly related to the operational performance of frequency-doubling devices, and then affects the high quality of laser output. In this paper, fixed abrasive polishing of LBO crystal specific lattice plane(θ=90°, φ=13.8°) using non-water based slurry is firstly developed. The main research work and results are as follows:(1) Three conditioning methods for fixed abrasive lapping pad were compared, and the lapping process of LBO crystal specific lattice plane was optimized. Conditioning with SiC-stone followed by adding unbonded SiC was determined, which can efficiently repair the cutting function of lapping pad and reduce scratch damage. The surface roughness Sa of lapped workpiece is 9.25 nm, and material removal rate is 481 nm/min when the lapping pressure is 28 kPa.(2) Fixed abrasive polishing pad with suitable hardness and abrasive type was selected. In acid water-based slurries, pH regulators and pH value were optimized step by step in order to analyze the mechanism which happens between LBO crystal specific lattice and chemical function of slurry. Citric acid owned the most suitable chemical activity, followed by lactic acid, oxalic acid and acetic acid. With the increase of citric slurry pH, surface roughness fallen down initially, then rose up. The surface roughness Sa of LBO crystal is down to 0.32 nm, and material removal rate is 366 nm/min with acid slurry pH=5.0.(3) Solvent of non-water based slurry was selected. Component and concentration of chemical additives were optimized through single factor method. With the increase of its concentration, all the surface roughness obtained by alcohol-based slurries, added with lactic acid, hydrogen peroxide and deionized water respectively, fallen down initially, then rose up, and the material removal rate ascended basically. The best surface quality was obtained with concentration of 25 vol.%, 5 vol.% and 15 vol.% respectively.(4) Orthogonal experiments were conducted to optimize the non-water based slurry and process parameters. Polishing pressure is a principal factor that affects the polishing quality largely. Lactic acid and hydrogen peroxide play roles in corrosion and corrosion inhibition respectively, which need deionized water to provide suitable ionization environment yet. The optimal scheme is 16 vol.% deionized water, 21 kPa polishing pressure, 22 vol.% lactic acid, 5 vol.% hydrogen peroxide, which makes non-water based polishing of LBO crystal specific lattice come true with surface roughness Sa 0.62 nm and material removal rate 392 nm/min.