Experimental study on size effect of tool edge and subsurface damage of single crystal silicon in nano-cutting

A method for fabricating a diamond tool with controllable edge radius was proposed. Using diamond tools with different edge radii at a low speed, nano-cutting tests were performed on single crystal silicon using a special instrument with SEM online observation. The chip morphology and deformation coefficient were analyzed to study the size effect of tool edge in the ductile-cut region. Electron back-scattered diffraction and laser micro-Raman spectroscopy were employed to detect subsurface damage in the machined silicon. The results indicated that the cutting-induced amorphous layer thickness is strongly dependent on the depth of cut and tool edge radius. In the beginning, the amorphous damage layer thickness decreases rapidly with the depth of cut, and then it increases gradually with the further increase in the depth of cut. The minimum amorphous damage can be obtained when the depth of cut is comparable to the tool edge radius.     

Electronically induced desorption; A specific localized radiation damage effect on surfaces

A survey is given of the effects of radiation (electrons, photons; to some extent ions) on surface layers which show up through liberation of particles (ions and neutrals) as a consequence of primary electronic excitations. It is shown that the observed characteristics of these effects (thresholds at valence as well as at core ionization energies, wide variations of cross sections with small changes of bonding to the surface, changing ion/neutral ratios, narrowly focussed angular distributions of ions and even of neutrals, energy distributions ranging up to 10 eV for ions and to 2 eV for neutrals, strong isotope effects) can be understood from rather general mechanisms with some common properties: A primary electronic excitation is followed by a rapid electronic rearrangement which can lead to transfer of energy from the electronic to the nuclear motion and which competes with delocalization of the energy. The total cross-sections and branching ratios can be determined by each of these factors. The relevance to radiation damage in ultramicroscopy may lie in the fact that here, too, transfer of electronic to nuclear motion is necessary for damage to occur, that again the competition of this transfer with delocalization of the primary excitation determines the overall efficiency of the damage process, and that therefore the resulting damage probabilities can be very different from the primary excitation cross-sections.     

Fundamental investigation of subsurface damage in single crystalline silicon caused by diamond machining

Single crystalline silicon was plunge-cut using diamond tools at a low speed. Cross-sectional transmission electron microscopy and laser micro-Raman spectroscopy were used to examine the subsurface structure of the machined sample. The results showed that the thickness of the machining-induced amorphous layer strongly depends on the tool rake angle and depth of cut, and fluctuates synchronously with surface waviness. Dislocation activity was observed below the amorphous layers in all instances, where the dislocation density depended on the cutting conditions. The machining pressure was estimated from the micro-cutting forces, and a subsurface damage model was proposed by considering the phase transformation and dislocation behavior of silicon under high-pressure conditions.     

The influence of grit size and stone pressure on honing

The internal honing of a steel workpiece (080 M 40) was investigated using three different grit sizes and a range of stone pressures. Metal removal rate, stone wear and surface finish were recorded. The results show that changes in stone pressure have a significant influence on the metal removal rate and the stone wear. It was also found that the surface finish of the workpiece was largely dependent on the grit size and independent of the stone pressure     

The effect of subsurface topography on secondary electron images from chromate pretreated aluminium surfaces

In secondary and scanning transmission electron microscopes, secondary electron images of surface films can be dominated by an image derived from electrons back-scattered from the interface between the film and the substrate. The extent of the domination has been established by studying the variation in image obtained using primary beams of different energy and by platinum coating to enhance surface secondary electron emission. Studies of thicker films also established that chemical or structural difference within a film also lead to imaging effects. In general, 5 keV electrons are the most effective in producing subsurface and structural or chemical imaging effects.     

Mechanisms of material removal and subsurface damage in fixed-abrasive diamond wire slicing of single-crystalline silicon

Single-crystal silicon was sliced using a newly developed high-speed fixed-abrasive dicing wire saw. The effects of diamond grit size, wire speed, and number of slicing cycle on the surface roughness and subsurface damage of the workpiece were investigated by surface profiling, Raman spectroscopy and cross-sectional transmission electron microscopy. It was found that by using finer diamond grits and increasing the sawing cycles, the depth of micro dents and saw marks was reduced significantly, and in turn, the surface roughness was improved. A transition from brittle mode to ductile mode machining was confirmed from chip morphology observation when reducing the grit size. The subsurface damaged layers were composed of amorphous layers, dislocated layers with grain boundaries, as well as micro cracks. The smooth surface regions were dominated by amorphous silicon; while within the saw marks, a mixture of amorphous and metastable silicon phases was detected. Inside the micro dents, however, single-crystal silicon was predominant. Furthermore, the significance of silicon amorphization and poly-crystallization was strongly dependent on the wire speed. The higher the wire speed, the less the amorphous and polycrystalline layer. The present study provides comprehensive insights into the surface formation mechanism which is important for process optimization of high-speed and low-damage slicing of single-crystal silicon.     

The effect of the size of the nominal area on the contact behaviour of surfaces

Experiments on the load/separation of rough flat surfaces show that the nominal area can be of primary significance in defining the behaviour. With large nominal areas the behaviour is independent of the actual size of the area and the results correlate with theoretical predictions based on statistical arguments. It is observed that the rougher the surface the larger the nominal area required for this to be true. With smaller nominal areas no unique behaviour is observed, the stiffness of the texture being a function of the actual nominal area. In such cases the experimental results correlate with a theoretical argument based on a discrete analysis of small samples of asperities.     

Forced-based tool deviation induced form error identification in single-point diamond turning of optical spherical surfaces

In the single-point diamond turning (SPDT) of optical spherical/aspheric surface, tool deviating from the spindle rotation center significantly deteriorates the form accuracy of the spherical/aspherical surface and its optical performance. In this study, the influence of tool deviation on the form accuracy of a convex spherical surface and the cutting force forms during the turning process were studied first, following which a force-based tool deviation model was derived to identify the tool deviation using cutting force. Finally, by analyzing the influence of tool deviation on the three-dimensional (3D) form of residual structures at the center of the convex spherical surface, the 3D form of the convex spherical surface was predicted online. Results indicate the existence of a mapping relation between the tool deviation and the cutting force form, which could be further used to online predict the 3D form of the machined convex spherical surface in SPDT through the established geometric model.     

磁流变抛光消除磨削亚表面损伤层工艺研究

针对传统光学制造技术对亚表面控制局限性和磁流变抛光的特点,提出用磁流变抛光替代研磨工序直接衔接磨削工序的新工艺流程。采用自研的磁流变抛光机床KDMRF−1000和水基磁流变抛光液KDMRW-2进行了磁流变抛光去除磨削亚表面损伤层的实验研究。直径为100mm的K9材料平面玻璃,经过156min的磁流变粗抛,去除50um深度的亚表面损伤层,表面粗糙度Ra值提升至0.926nm,经过17.5min磁流变精抛,去除了200nm深度的材料,并消除磁流变粗抛产生的抛光纹路,表面粗糙度Ra值提升至0.575nm。应用磁流变抛光可以高效消除磨削产生的亚表面损伤层。磁流变抛光替代研磨工序直接衔接磨削工序的新工艺流程可以实现近零亚表面损伤和纳米精度抛光两个工艺目标。     

Influence of grain size on the wear behavior of CVD diamond coatings in micro-EDM

In order to reduce wear and therewith enhance the microelectrical discharge machining (µ-EDM) results, a coated electrode was used. The paper presents the results of investigations into the influence of grain size of the boron-doped CVD diamond coating on the wear behavior in microsinking EDM. Experimental investigations show that nanocrystalline coatings exhibited smaller discharge craters compared to those for microcrystalline diamond coatings, and microcrystalline coating showed melted material around the discharge crater. The finding will be subjected to further investigations.     

Investigation of subsurface damage considering the abrasive particle rotation in brittle material grinding

This paper presents the feasibility study of potential application of recently developed surface defect machining (SDM) method in the fabrication of silicon and similar hard and brittle materials using smooth particle hydrodynamics (SPH) simulation approach. Simulation study of inverse parametric analysis was carried out to determine the Drucker-Prager (DP) constitutive model parameters of silicon by analysing the deformed material response behaviour using various DP model parameters. Indentation test simulations were carried out to perform inverse parametric study. SPH approach was exploited to machine silicon using conventional and surface defect machining method. To this end, we delve into opportunities of exploiting SDM through optimised machining quality, reduced machining time and lowering cost. The results of the conventional simulation were compared with the results of experimental diamond turning of silicon. In the SPH simulations, various types of surface defects were introduced on the workpiece prior to machining. Surface defects were equally distributed on the top face of the workpiece. The simulation study encompasses the investigation of chip formation, resultant machining forces, stresses and hydrostatic pressure with and without SDM. The study reveals the SDM process is an effective technique to manufacture hard and brittle materials as well as facilitate increased tool life. The study also divulges the importance of SPH evading the mesh distortion problem and offer natural chip formation during machining of hard and brittle materials.     

Influence of crystal anisotropy on subsurface damage in ultra-precision cylindrical turning of CaF2

An optical microcavity, which stores light at a certain spot, is an essential component to realize all-optical signal processing. Single-crystal calcium fluoride (CaF₂) theoretically shows a high Q-factor which is a desirable optical property. The CaF₂ microcavity can only be manufactured by ultra-precision cylindrical turning (UPCT). The authors have studied UPCT of CaF₂ and shown the influence of crystal anisotropy and tool geometry on surface roughness and subsurface damage. The study indicated that a smaller nose radius of the cutting tool led to shallower subsurface damage. Thus, it is inferred that a smaller nose radius compared to the previous nose radius (0.05 mm) can further reduce subsurface damage. Nevertheless, the mechanism that causes a difference in subsurface damage due to crystal anisotropy is not sufficiently clear. The influence of subsurface damage on microcavity performance is still unclear. In this study, the UPCT of CaF₂ was conducted using a tool with a nose radius of 0.01 mm. The subsurface damage was investigated by transmission electron microscope (TEM) observation from the viewpoint of the change in crystal lattice arrangement. In our previous study, fast Fourier transfer (FFT) analysis was used for confirmation of change of crystal structure. In this study, FFT analysis was also used to quantitatively evaluate the depth of subsurface damage. In addition, inverse fast Fourier transfer (IFFT) was used to analyze change of crystal lattice arrangement clearly, which enables discussion of the influence of slip systems. Finally, optical microcavities are manufactured without any crack, and the influence of subsurface damage on microcavity performance is experimentally evaluated using a wavelength tunable laser and power meter.     

Modeling the edge contact effect of finite contact lines on subsurface stresses

Finite contact line conditions lead to subsurface stress distributions determined by the free boundaries. Combined with a correction procedure, Semi-Analytical Methods (SAMs) accurately include the free boundary effects, and represent a rapid alternative to the Finite Element Method (FEM) for contact pressure calculation. This paper extends the free boundary correction procedure to the evaluation of surface and subsurface stresses from SAMs. The investigation integrates a validation based on a two-level factorial comparison confronting the stress distributions established with the developed procedure to results obtained from FEM models. The comparison examines three dimensionless factors, and shows that the stress distributions are evaluated with a high level of precision. The model also offers evaluation more than 125 times faster than FEM simulations.     

The effect of detector size on the extinction coefficient in confocal polarization microscopes

We consider the effect of detector size on the polarization extinction coefficient in three geometries of confocal microscopes. We find that a single mode optical fibre-based reciprocal system employing circularly polarized light offers great ease of alignment together with an extremely high extinction coefficient.     

The effect of surface films on the static contact of rough flat surfaces

The study of contact phenomena of solid surfaces, such as the electrical and thermal conductance across interfaces, friction and wear, fluid leakage through seals and the stiffness of joints, is of vital importance in many engineering applications. The effect of surface films, such as oxides of the metal, oils and grease, on the behaviour of two surfaces in contact under a normal load has been studied. The contact behaviour has been quantitatively assessed by measuring the normal approach of two surfaces in contact; a capacitance technique was employed for the measurement of displacements. Theoretical analyses are presented for determining the normal approach as a function of load. The various statistical parameters of surfaces relevant to such analyses are also presented. It has been demonstrated that the presence of surface films enhances the stiffness of deformable surfaces.     

光学材料研磨亚表面损伤快速检测及其影响规律研究

基于印压断裂力学理论,针对光学材料研磨加工过程建立了亚表面损伤深度与表面粗糙度间关系的理论模型,以实现亚表面损伤深度的快速、准确和非破坏性检测。使用磁流变抛光斑点技术测量了K9玻璃在不同研磨条件下的亚表面损伤深度,对上述理论模型进行实验验证。最后,分析了研磨加工参数对亚表面损伤深度的影响规律,提出了以提高光学零件加工效率为目的的研磨加工策略。研究表明：光学材料研磨后亚表面损伤深度与表面粗糙度成单调递增的非线性关系,该幂函数的幂为4/3。磨粒粒度对亚表面损伤深度的影响最显著,研磨盘硬度的影响次之,而研磨压力和研磨盘公转速度的影响基本可以忽略。     

The effect of fluoride therapies on the morphology of bleached human dental enamel

The aim of this in vitro study was to evaluate qualitatively the surface morphology of enamel bleached with 35% hydrogen peroxide (HP) followed by application of fluoridated agents. Forty intact pre molars were randomly distributed into four groups (n = 10), treated as follows: Group I (control group) remained stored in artificial saliva at 37 °C, Group II - 35% HP; Group III - 35% HP + acidulated fluoride (1.23%) and Group IV - 35% HP + neutral fluoride (2%). The experimental groups received three applications of bleaching gel and after the last application all specimens were polished. This procedure was repeated after 7 and 14 days, and during the intervals of applications, the specimens were stored in artificial saliva at 37°C. Scanning electron microscopy (SEM) analysis showed superficial irregularities and porosities to varying degrees in bleached enamel compared to control group. Sample evaluation was made by attributing scores, and data were statistically analyzed using Kruskal-Wallis and Dunn tests (P < 0.05). SEM qualitative investigation demonstrated that 35% hydrogen peroxide affected human dental enamel morphology, producing porosities, depressions, and superficial irregularities at various degrees. These morphological changes were higher after the application of 1.23% acidulated fluoride gel.     

基于Monte Carlo的定量光导荧光仿真分析

定量光导荧光技术（QLF）是一种利用龋损组织光学参数变化引起组织内光能重新分布这一现象的龋齿早期诊断技术。利用Monte Carlo随机统计方法对所建龋齿模型中μssound=15／mm,μscaries=（30、60、100、150、200、250、300）／mm七种情况进行了仿真,获得出射表面光能量相对分布图,并对其分析,结果表明病损区总的荧光损失量与散射系数成正比,拟合结果显示,两者具有线性关系。