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KDP晶体不同加工表面损伤检测与损伤机理分析
Damage Detection of Different Machined Surface and Damage Mechanism Analysis of KDP Crystal
【作者】 王奔；
【导师】 吴东江；
【作者基本信息】 大连理工大学 ， 机械制造及其自动化， 2008， 硕士
【摘要】 KDP（磷酸二氢钾,KH2PO4）晶体,因其具有较大的电光和非线性光学系数、高的激光损伤阈值、低的光学吸收系数、高的光学均匀性和良好的透过波段等特点而被广泛应用于激光变频、电光调制和光快速开关以及惯性约束核聚变等高技术领域。随着科学技术的不断发展,要求这种功能晶体器件的尺寸规格越来越大,厚度要求越来越薄,加工精度和表面完整性也越来越高。然而,由于KDP晶体具有易潮解、硬度低以及各向异性等特性,是目前公认的难加工材料之一。KDP晶体的加工通常包括切割、车削、磨削、抛光等。磨削是KDP晶体常用的加工方法之一,但由于磨削过程中影响表面质量的因素较多,为有效的提高磨削加工质量,对KDP晶体磨削去除机理及磨削产生的表面及亚表面损伤的检测是十分必要的。本文在阅读大量参考文献的基础上,参考硬脆材料的研究方法,对KDP晶体的加工损伤进行了研究。利用光学显微镜及SEM等设备对由切割、研磨、抛光及磨削等加工后的KDP晶体表面进行观测;利用截面法、择优蚀刻法及角度抛光法对切割、研磨及磨削加工后的KDP晶体亚表面损伤进行了研究。同时,研究了各向异性及进给量对磨削表面层质量的影响,并通过划痕实验对KDP晶体磨削加工损伤机理进行了实验研究。通过以上研究得到如下结论:不同加工方法加工出的试件表面质量及亚表面损伤均有所不同;不同晶向上磨削表面质量及划痕表面层损伤均存在差异。由金刚石线切割产生的裂纹深度为85.59μm,利用#3000砂纸研磨后的晶体损伤深度为19.32μm。通过选择合适的抛光液及清洗方法,抛光表面粗糙度达到1.556nm。采用#600砂轮自旋转磨削,当进给量分别为10μm/min和40μm/min时,磨削所产生的亚表面最大损伤深度值分别为7.41μm和8.96μm。采用平面磨削时,沿（001）晶面不同晶向磨削后的晶体表面质量也呈现出一定的各向异性。KDP晶体（001）晶面划痕实验表明,随着径向力的增加,划痕表面从塑性去除为主转变到脆性去除为主;亚表面首先产生大量位错然后出现中位及横向裂纹,从而导致晶体损伤深度的增加及材料的脆性去除。同时,不同晶向上表面裂纹扩展方向、摩擦系数以及亚表面裂纹形状、损伤深度、位错腐蚀坑形状均存在较大的差异。
【Abstract】 KDP（Potassium dihydrogen phosphate,KH2PO4） crystal,based on its biggish electro-optic and non-linear optical coefficient,higher laser damage threshold,lower optical absorption coefficient,higher optical uniformity and suitably transparent wave band,is widely used in high tech fields,such as laser frequency conversion,electro-optic modulation, optical speediness switch,inertia control fusion and so on.With the development of science and technology,KDP crystal requires larger and thinner,machining accuracy and surface integrity also requires higher.However,it’s well-known that KDP crystal is one of most difficult machining materials because it has several disadvantages such as soft,fragile, hygroscopic and anisotropy.Such as cutting,turning,grinding and polishing are common methods in KDP crystal mahining.Grinding is one of machining method in KDP crystal processing.Because grinding is a complicated mechanical process,many factors can influence the surface quality,so it is necessary to study the removal mechanisms of KDP crystal grinding and the damage detection of machined surface in order to improve the quality of grinding.Based on lots of references read and reference the method used on hard and brittle materials,the machining damage of KDP crystal was investigate in this paper.Such as optical microscope and SEM were used to detect the surface machined by cutting,lapping,polishing and grinding;cross section,selective etching and angle polishing were used to study the subsurface damage generated by cutting lapping and grinding.Besides,the influence of anisotropy and feed to quality of grinding surface were studied,scratch experiment was taken to investigate the damage mechanism of KDP crystal.The results indicated that:the surface quality and subsurface damage were different on differents machined surface;both the surface quality and the scratch damage of surface layer were different with the change of crystal orientation.The depth of subsurface damage of cutting by diamond wire and lapping by #3000 abrasive papers was 85.59μm and 19.32μm, respectively.When the polishing slurry and the cleaning method of polished surface were suitable,surface roughness reached 1.556nm.When KDP crystal was machined by rotational grinding with #600 grinding wheel,the subsurface damage depth was 7.41μm and 8.96μm corresponding to the feed was 10μm and 40μm.Anisotropy was showed by the ground surface quality machined in different orientation in method of surface grinding on（001） crystal plane.Scratch experiment on（001） plane of KDP crystal showed that:with the increase of radial force,surface deformation changed from the region of mainly plastic to the region of mainly brittle along the scratch;subsurface damage changed from dislocation to middle crack and transverse crack so that the damage of crystal was increased and made material removal in brittle mode.The orientation of scratch crack propagate,friction coefficient on surface and the shape of crack,depth of damage,etching pit of dislocation in subsurface were different with the change of scratch direction.