铌酸锂晶体的研磨亚表面损伤深度

针对光学材料研磨过程引入的亚表面损伤层(SSD)深度对工件的抛光工序效率和表面质量的影响,探索了光学材料在研磨过程中的亚表面损伤规律。采用角度抛光的方法测量了软脆材料铌酸锂(LN)晶体的损伤层深度,分析了研磨方式、磨粒粒径和研磨压力对工件亚表面损伤层的影响规律。结果表明:研磨方式对损伤缺陷的影响最为显著,相同研磨条件下游离磨料研磨后的损伤层深度约为固结磨料研磨的3~4倍,游离磨料研磨后工件亚表面存在多处圆弧形裂纹,固结磨料研磨后主要显现细小裂纹和"人"字型裂纹;当磨粒粒径从W28下降到W14后,游离研磨的亚表面损伤层深度下降至原来的45%,而固结研磨的损伤层深度下降至30%;另外,研磨压力的降低有利于减小工件的亚表面损伤。该研究对LN晶体研磨方式及研磨工艺的选择具有指导意义。

Subsurface damage depth of lithium niobate crystal in lapping

In consideration of the effect of the Subsurface Damage Depth (SSD)of optical material introduced by lapping on the efficiency of polishing process and surface quality of workpieces, this paper explores laws of the subsurface damages (SSDs) of optical materials in lapping process. An angle polishing method was employed to measure the SSD of a soft-brittle material Lithium Niobate (LN) crystal. The influences of lapping type, grit size and lapping parameter on the SSD were investigated experimentally. The results show that lapping method is the most significant factor on the SSD. The SSD of loose abrasive lapping is about 3-4 times that of fixed abrasive lapping in the same condition. Circular cracks are filled in the subsurface of loose abrasive lapping workpiece, while herringbone cracks are mainly distributed over the subsurface of fixed abrasive lapping workpiece. The effects of grit size are also quit remarkable.With the grit size decreasing from W28 to W14, the damage depths of loose abrasive lapping and fixed abrasive lapping are decreased to 45% and 30%, respectively. Moreover,reducing applied load is beneficial to subsurface defects. This study affords a guidance for lapping method selection and lapping process optimization of LN crystals.