Nanomechanical characterization of RB-SiC ceramics based on nanoindentation and modelling of the ground surface roughness

Reaction bonded silicon carbide (RB-SiC) ceramics are the primary structure and mold materials for the optical industry and mostly are machined by means of ultra-precision grinding to achieve a satisfactory surface quality. However, it is not easy to attain the theoretical prediction of surface quality, particularly surface roughness, because of different mechanical characterization of Si/SiC phases inside the RB-SiC ceramics. In this work, the nanoindentation tests were performed to investigate the nanomechanical characterization of individual phase inside the RB-SiC ceramics. On the basis of the nanoindentation results of RB-SiC, a theoretical model was established to predict surface roughness in the ultra-precision grinding process, which considered the different removal mechanisms of Si matrix and SiC particles. The comparison of the prediction results of existing and novel models and single-factor experimental results shows that the novel model was well consistent with the experiment.     

双面研磨抛光中工件表面“塌边现象”的研究

随着信息产业的迅速发展,对半导体器件、光学器件等的表面平整度提出了越来越高的要求。双面研磨/抛光技术是能使工件得到较高形状精度和表面精度的超精密加工主要方法。但是在双面研磨抛光加工中工件存在"塌边现象",这导致工件的表面平整度变差。本文对双面研磨抛光中工件"塌边"这一问题进行研究,分析造成工件表面"塌边"的各种因素,以及相应解决方法,对进一步提高双面研磨抛光加工质量具有重大意义。     

Vibration-assisted dry polishing of fused silica using a fixed-abrasive polisher

Glass is a ubiquitous but essential material in everyday life and industry. The most common method for polishing glass involves the use of free abrasives. However, this method is basically non-deterministic and lacks efficiency. Therefore, vibration has been employed to aid fixed-abrasive polishing in our research. It is found that the vibration can increase the material removal rate while maintain surface quality in fixed abrasive polishing. Normalized Preston coefficients that are the index of the polishing capability of a certain polishing process considerably increase in vibration-assisted polishing process. A mathematic model is set up to interpret the increase in material removal rate for vibration process. The modeled results show that the vibration can improve material removal by increasing vibration amplitude in vertical direction while the horizontal vibration contributes little to increasing material removal rate, which agrees well with experimental results. Aside from material removal, surface morphology of polished glass was also modeled for both vibration and conventional processes. Both experimented and simulated morphology evidence that the vibration some periodic structure on polished surface. The possible mechanism in dry fixed abrasive polishing was also chemically analyzed and a probable mechanism is put forward to clarify the material removal in dry fixed abrasive polishing.     

Preparation of La-doped colloidal SiO2 composite abrasives and their chemical mechanical polishing behavior on sapphire substrates

Chemical mechanical polishing (CMP) has become a widely accepted global planarization technology. Abrasive is one of the key elements in CMP process. In order to enhance removal rate and improve surface quality of sapphire substrate, a series of novel La-doped colloidal SiO₂ composite abrasives were prepared by seed-induced growth method. The CMP performance of the La-doped colloidal SiO₂ composite abrasives on sapphire substrate were investigated using UNIPOL-1502 polishing equipment. The analyses on the surface of polished sapphire substrate indicate that slurries containing the La-doped colloidal SiO₂ composite abrasives achieve lower surface roughness, higher material removal rate than that of pure colloidal SiO₂ abrasive under the same testing conditions. Furthermore, the acting mechanism of the La-doped colloidal silica in sapphire CMP was investigated. X-ray photoelectron spectroscopy analysis shows that solid-state chemical reactions between La-doped colloidal SiO₂ abrasive and sapphire surface occur during CMP process, which can promote the chemical effect in CMP and lead to the improvement of material removal rate.     

Theoretical analysis on effects of grain size variation

Grinding wheels consist of abrasive grains, bonding materials and porous, which are specified by five factors; type of grain, size of grain, bonding material, bonding strength and grain concentration or volume fraction of grain. The grain size is represented by the mean diameter/radius of grains. However, the abrasives in a grinding wheel are randomly scraggly in size and shape. There is no particular aspect to regulate the variation in grain size. This paper addresses, via a theoretical analysis on the distribution of grain size, the average volume of a grain, the number of grains contained in a specific volume of the wheel, the number and protrusion distribution of grains exposed in a wheel working surface and the fraction of effective grain, when the grain size varies. The effect on the resultant finished surface roughness is also discussed.     

化学机械抛光中抛光垫材料的研究与展望

在化学机械抛光中,抛光垫的材料是重要影响因素之一,它直接影响着抛光效果。本文介绍了化学机械抛光垫的基本材料、材料特性及其对抛光效果的影响,目前化学机械抛光加工中所采用的抛光垫材料及主要用途,对各种抛光垫材料在抛光过程中存在问题进行了分析,同时展望了抛光垫材料的发展趋势。     

大粒径SiO2磨粒固结磨具加工蓝宝石试验研究

目的验证大粒径(30μm)SiO_2磨粒固结磨具加工蓝宝石晶片的有效性,优化磨具配方,为实现蓝宝石晶片高效、高质量、低成本加工提供有效参考。方法制作不同配方的氯氧镁结合剂SiO_2固结磨具加工蓝宝石,以去除率、表面粗糙度为评价指标,研究磨粒粒度、结合剂比例、磨粒含量对加工效果的影响。结果 6种不同粒径(均30μm)的SiO_2磨粒固结磨具加工蓝宝石,表面粗糙度均有改善,粒径越小,改善效果越好。结合剂中,活性Mg O、MgCl_2和H_2O三者的摩尔比会影响去除率和粗糙度。磨具磨粒的含量高,去除率高,粗糙度小。结论氯氧镁结合剂中,活性MgO:MgCl_2:H_2O的摩尔比为7:1:16,325#SiO_2为磨粒,磨粒质量占结合剂质量的60%,制作磨具加工蓝宝石,转速210 r/min,加载0.4 MPa,加工3 h,去除率为平均17μm/h,表面粗糙度Ra由初始平均345 nm改善至平均9 nm。     

圆柱滚子外圆研磨优化实验研究

为优化圆柱滚子外圆研磨,以正交试验研究工件偏角、工件位置及转速（包括上下抛光盘转速、偏心轮转速和外齿圈转速）对材料去除率、表面粗糙度和圆度的影响。结果表明:工件偏角对材料去除率的影响最显著,转速组合次之,工件位置最小;转速对表面粗糙度的影响最显著,工件偏角次之,工件位置最小;工件位置对圆度的影响最显著,转速组合次之,工件偏角最小。最佳条件为工件偏角0°、工件位置0.8,各转速值分别为-76、84、80和48 r/min。加工15 min后,圆柱滚子的材料去除率可达到0.541 μm/min;表面粗糙度由0.078 μm降至0.045 μm,比初始表面粗糙度降低42.3%;圆度由0.74 μm降至0.41 μm,比初始圆度降低44.6%。      

CMP behavior of alumina/metatitanic acid core–shell abrasives on sapphire substrates

The abrasive is one of the important influencing factors during the chemical mechanical polishing (CMP) process. Although α-alumina is one of the most commonly used sapphire polishing abrasives due to its high hardness, it often results in surface damage. To receive lower surface roughness and high material removal rate, a common approach is to modify the surface of alumina. In this work, a series of alumina/metatitanic acid composite abrasives with core–shell structure were synthesized. The CMP performances of the pure alumina and alumina/metatitanic acid core–shell abrasives on sapphire substrates were investigated after polishing under the same conditions. Experimental results indicate that the alumina/metatitanic acid core–shell abrasives can not only improve the surface quality, but also further enhance the material removal rate. Furthermore, through the X-ray photoelectron spectroscopy test, this study investigated the chemical effect mechanism of the alumina/metatitanic acid core–shell abrasives in sapphire CMP. The results show that solid-state chemical reactions occur between metatitanic acid shell and sapphire surface during CMP process. We also investigated the mechanical friction mechanism through abrasive wear and adhesive wear.     

基于单转盘变曲率沟槽研磨方法的球体加工试验研究

目的针对传统V形槽研磨方球体时自转角恒定、加工轨迹不能均匀包络整个球面而影响产品一致性的问题,提出一种单转盘变曲率沟槽球体研磨加工方法,使球体运动状态随沟槽曲率的变化而变化。方法基于纯滚动假设条件,通过几何运动学分析建立自转角与运动轨迹的关系模型,并自主研发了变曲率沟槽循环研磨机床,在该平台上对G16级GCr15钢球进行加工试验,改变研磨液、载荷、转速与研磨盘等工艺参数,经过粗磨、精磨和抛光三道工序,以球体圆度、粗糙度与批内一致性测量结果为指标,对单转盘变曲率沟槽的研磨效果进行评价。结果仿真结果表明,通过优化变曲率轨迹参数能实现球体表面加工轨迹的均匀全包络,轨迹均匀性标准差SD达到0.1986。球体抛光后,圆度均值为0.095μm,表面粗糙度均值为0.011μm,一致性达到了0.17μm,加工精度达到G5级球要求。结论沟槽滚道曲率的变化可使球体自转角在0?~90?之间持续变化,改变球体的运动姿态,获得全包络研磨轨迹,进而实现球体高效高一致性的加工,具有较强的工程应用价值。