Traditional Mechanical Polishing Research Articles

Vibratory polishing effects on passivity of 304L stainless steel surfaces

ABSTRACT Surface spectroscopy analysis and electrochemistry were applied to study the effects of surface preparation by vibratory polishing on the passivity of stainless steel 304L surfaces. Compared to grinding by traditional mechanical polishing, vibratory polishing promotes the enrichment of Cr(III) oxide and hydroxide species in the duplex chemical structure of the surface native oxide film by enhancing selective Fe oxidation and dissolution. As a result, spontaneous passivity, tested in aggressive sulphuric acid electrolyte, is enhanced. However, in the absence of enrichment in Mo(IV) and Mo(VI) species in the passive film, the Cr enrichment does not enhance passivity upon anodic polarisation nor increase the resistance to Cl-induced passivity breakdown and initiation of localised corrosion in accelerated testing conditions. The results provide comprehensive insight into the mechanisms underlying the passivity enhancement of stainless steel by surface engineering.

Scanning electron microscopic evaluation of broad ion beam milling effects to sedimentary organic matter: Sputter-induced artifacts or naturally occurring porosity?

Research examining organic-matter hosted porosity has significantly increased during the last decade due to greater focus on understanding hydrocarbon migration and storage in source-rock reservoirs, and technological advances in scanning electron microscopy (SEM) capabilities. The examination of nanometer-scale organic-matter hosted porosity by SEM requires the preparation of exceptionally flat geologic samples beyond the abilities of traditional mechanical polishing, which can deform or otherwise obscure organic surfaces. To meet this demand, broad ion beam (BIB) milling was introduced as a sample preparation technique for SEM petrographic analysis of geologic samples. As with any sample preparation technique, there can be unintended consequences. In this study, we examined the development of nanometer-scale sputter-induced voids caused by BIB milling of thermoset plastic binder material [poly(methyl methacrylate), PMMA] used for the mounting of geologic samples, and artifact sputter-induced voids in the organic matter of Green River Formation and Kimmeridge Clay Formation source rocks. Development of artifact sputter-induced voids was evaluated in relation to variations in the slope of the sample examination surface (0.0–4.9% slope), effectively varying the angle of ion incidence. The results indicate that only minor variations in the angle of ion incidence can generate sputter-induced voids in both PMMA (10.0–386.2 nm diameter sputter-induced voids) and sample sedimentary organic matter (solid bitumen; 12.2–103.6 nm diameter sputter-induced voids). Overall, average artifact pore diameters increased with increasing ion incidence angle within PMMA. Although sputter-induced voids within solid bitumen in the Green River Formation sample were only found in limited extent, the size of these void artifacts falls within the same size range as naturally occurring meso-macroporosity. That is, the pore-like artifacts could easily be misconstrued as naturally developed organic porosity, which is a major concern for SEM-based porosity evaluation methods. This study describes the factors that contribute to the creation of artifact sputter-induced voids, their distinguishing characteristics, and best practices for avoiding the creation of ion-induced artifacts.

Artifact-Free Microstructures in the Interfacial Reaction between Eutectic In-48Sn and Cu Using Ion Milling.

Eutectic In-48Sn was considered a promising candidate for low-temperature solder due to its low melting point and excellent mechanical properties. Both Cu2(In,Sn) and Cu(In,Sn)2 formation were observed at the In-48Sn/Cu interface after 160 °C soldering. However, traditional mechanical polishing produces many defects at the In-48Sn/Cu interface, which may affect the accuracy of interfacial reaction investigations. In this study, cryogenic broad Ar+ beam ion milling was used to investigate the interfacial reaction between In-48Sn and Cu during soldering. The phase Cu6(Sn,In)5 was confirmed as the only intermetallic compound formed during 150 °C soldering, while Cu(In,Sn)2 formation was proven to be caused by room-temperature aging after soldering. Both the Cu6(Sn,In)5 and Cu(In,Sn)2 phases were confirmed by EPMA quantitative analysis and TEM selected area electron diffraction. The microstructure evolution and growth mechanism of Cu6(Sn,In)5 during soldering were proposed. In addition, the Young's modulus and hardness of Cu6(Sn,In)5 were determined to be 119.04 ± 3.94 GPa and 6.28 ± 0.13 GPa, respectively, suggesting that the doping of In in Cu6(Sn,In)5 has almost no effect on Young's modulus and hardness.

Parameter Optimization of RB-SiC Polishing by Femtosecond Laser

Reaction-boned silicon carbide (RB-SiC) is considered a new material for large lightweight ground-based space telescopes due to its high specific stiffness, low thermal deformation, and excellent optical quality. The excellent mechanical properties of RB-SiC result in the low efficiency of traditional polishing and mechanical polishing. In this paper, a polishing method for RB-SiC based on a femtosecond laser is proposed to improve surface quality. A theoretical heat conduction model was established in the process of femtosecond laser irradiation of SiC. We analyzed the ablation type and calculated the single-pulse ablation threshold of SiC, which verified the feasibility of femtosecond laser polishing. Further, the effects of polishing parameters on the polished surface quality were analyzed by a series of experiments, and the optimal parameters were selected. It was observed to improve polishing efficiency and can replace the intermediate steps of traditional mechanical polishing.

Study on Polishing of Polycrystalline AlN Using Sol–Gel Polishing Tool

Polycrystalline aluminum nitride has extensive application prospects in substrate materials, insulating layer materials, and packaging materials. Polycrystalline aluminum nitride is sintered from powder. The traditional mechanical polishing method is easy to cause aluminum nitride grains to fall off to form pits. In this paper, to improve the polishing effect, based on the hydration of polycrystalline aluminum nitride, a sol-gel (SG) polishing tool was proposed to polish polycrystalline aluminum nitride. The polishing process was divided into rough polishing and fine polishing. The diamond particle size of the SG tool used for rough polishing was <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$40\mathbf {\mathrm {\mu }}\text{m}$ </tex-math></inline-formula> . The diamond particle size of the SG tool used for fine polishing was <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5\mathbf {\mathrm {\mu }}\text{m}$ </tex-math></inline-formula> . Moreover, the polycrystalline AlN was processed with or without deionized water. The results showed that in the rough polishing stage, the material removal rate (MRR) of the polishing method without deionized water was four times higher than that of the polishing method with deionized water. However, in the fine polishing stage, the MRR of the polishing method with deionized water was slightly higher than that of the polishing method without deionized water. The results showed that mechanical removal is the primary material removal method in the rough polishing stage. In the fine polishing stage, hydration can improve the polishing effect of polycrystalline aluminum nitride.

Surface smoothing of bulk metallic glasses by femtosecond laser double-pulse irradiation

Bulk metallic glasses (BMGs) with amorphous structure have excellent mechanical and chemical properties. In polishing process, it is hard but important to maintain amorphous state to keep original properties of BMGs, which are easily crystallized in traditional mechanical polishing and long-pulse laser polishing. In this paper, we first propose to use femtosecond laser double-pulse irradiation to smooth the surface of Zr-based BMG and make it free of laser-induced periodic surface structures and crystallization. Here, the smooth surface with half decreasing in roughness (Sa) to 111 nm is achieved by optimized parameters with laser pulse energy 0.06 μJ of the first pulse, energy ratio 40% of the first to the second pulse and time delay 20 ps. Obvious transition from a coarse surface to a smooth one occurs at near 10 ps time delay and 40% energy ratio. Mobility enhancement of molten materials guarantees the removal of undesirable surface structures through surface tension and gravity. Crystallization is avoided due to rapid heating and cooling under femtosecond laser double-pulse irradiation. A smoothed BMG surface obtained by this method verifies its feasibility in BMGs polishing.

High-quality plasma-assisted polishing of aluminum nitride ceramic

Aluminum nitride (AlN) easily reacts with water when polished using an aqueous slurry. Moreover, grains tend to easily shed off of the AlN surface since it is a sintered material. Thus, obtaining a smooth AlN surface by traditional mechanical polishing techniques is challenging. Herein, we demonstrate plasma-assisted polishing (PAP) that relies on surface modification by plasma irradiation and removal of the modified layer by ultra-low pressure. After CF4 plasma irradiation, AlN was modified to AlF3, and its modified layer was removed using a diamond abrasive. The material removal rate increased twice by CF4 plasma irradiation compared with that without it.

Formation mechanism of a smooth, defect-free surface of fused silica optics using rapid CO2 laser polishing

Surface defects introduced by conventional mechanical processing methods can induce irreversible damage and reduce the service life of optics applied in high-power lasers. Compared to mechanical processing, laser polishing with moving beam spot is a noncontact processing method, which is able to form a defect-free surface. This work aims to explore the mechanism of forming a smooth, defect-free fused silica surface by high-power density laser polishing with coupled multiple beams. The underlying mechanisms of laser polishing was revealed by numerical simulations and the theoretical results were verified by experiments. The simulated polishing depth and machined surface morphology were in close agreement with the experimental results. To obtain the optimized polishing quality, the effects of laser polishing parameters (e.g. overlap rate, pulse width and polishing times) on the polishing quality were experimentally investigated. It was found that the processing efficiency of fused silica materials by carbon dioxide (CO2) laser polishing could reach 8.68 mm2 s−1, and the surface roughness (Ra) was better than 25 nm. Besides, the cracks on pristine fused silica surfaces introduced by initial grinding process were completely removed by laser polishing to achieve a defect-free surface. The maximum laser polishing rate can reach 3.88 μm s−1, much higher than that of the traditional mechanical polishing methods. The rapid CO2 laser polishing can effectively achieve smooth, defect-free surface, which is of great significance to improve the surface quality of fused silica optics applied in high-power laser facilities.

A New Vibration Device Applied for Two-Dimensional Ultrasonic Polishing of Biomaterials

For the research of the performance of two-dimensional ultrasonic polishing (TDUP) on the biomaterials, a new vibration device was designed. Meanwhile, our aim is to study the mechanism of multiangle polishing to cope with the complex structure of biomaterials. The device is composed of piezoelectric rings, asymmetric transformer, ultrasonic generator, and so on. The structural dimension parameters were optimized by finite element analysis, and especially the groove size on the transformer was discussed in detail. Two kinds of experiments had been conducted to test the performance of the proposed device, including impedance analysis experiments and amplitudes measurement experiments. Furthermore, a mechanical model to explain the principle of the multiangle polishing was set up, which could assist to analyze the influence of different polishing angles in terms of machining. Finally, the machining experiments and multiangle polishing experiments were carried out to verify the effectiveness of the device. Compared with traditional mechanical polishing, the surface roughness is reduced from 235 nm to 140 nm. The results of multiangle polishing experiments indicate that the surface quality of biomaterials will be prominently affected by different polishing angles. In addition, the polishing mechanism will transform owing to the inversion of the normal velocity during the polishing process with the angle increasing. The surface morphology will also be affected. It has been proven that the experimental results agree with the model well.

Reflectance increase from broad beam ion milling of coals and organic-rich shales due to increased surface flatness

Broad ion beam (BIB) milling is useful in organic petrology because it can yield flat sample surfaces and avert the ‘smearing’ of organic matter (OM) that results from traditional mechanical polishing. This potentially makes BIB especially useful in the study of nano-porosity, where even minor mechanical disruption of the sample surface distorts the sample characteristic of interest—the pore structure. However, several studies have observed an OM reflectance increase after BIB milling, concluding that ion milling may cause thermal alteration to OM surfaces. To better understand ion milling effects on organic matter, coal (subbituminous, high volatile bituminous, medium volatile bituminous, anthracite) and shale [Bakken Formation, Ohio Shale-Huron Member (5), Kimmeridge Clay Formation, Alum Shale, New Albany Shale] samples were prepared using traditional mechanical polishing methods. Reflectance measurements (% Ro) were gathered on all maceral types present before BIB milling, followed by re-measurement of OM reflectance at the same locations after milling. Most OM increased in reflectance after BIB milling, with some exceptions in high maturity samples. Liptinite macerals in both coal and shale samples showed the greatest percent reflectance increase on average (+133%; n = 338), followed by solid bitumen (+49%; n = 313), vitrinite (+26%; n = 413), and inertinite (+9%; n = 220). Despite the increases to OM reflectance caused by BIB milling, no evidence was found for kerogen conversion (e.g., change in maceral abundances), or for migration of newly generated petroleum (e.g., pseudomorphic replacement of kerogen by solid bitumen). Such changes occur when samples are thermally altered from immature conditions into the oil window (e.g., by hydrous pyrolysis), and, if the increases in OM reflectance were thermally driven (by BIB milling), they should have been observed in the above experiments. Herein, we also used atomic force microscopy to document a decrease in surface roughness of correlative locations of OM on pre- and post-ion milled samples. This improved surface polish caused by BIB milling appears to be the root cause of increased OM reflectance, as no other supporting evidence of thermal alteration could be found. That is, the fraction of light formerly lost to oblique scatter in diffuse reflectance from a mechanically polished surface is converted to specular reflectance after BIB ion milling. Thus the light leaves the surface at a near normal angle and returns to the detector, resulting in increased OM reflectance.

Blind evaluation of AFM tip shape by using optical glass surface with irregular nanostructures as a tip characteriser

Atomic-force microscopy (AFM) is a type of scanning probe microscopy. It possesses nano-scale resolution which is >1000 times better than the optical diffraction limit. An image of AFM is the result of interaction between the tip and the sample. The AFM image is not accurate and distorted due to the finite size of the probe tip. To correct the AFM image and acquire accurate sample morphology information, it needs to evaluate the tip shape and status. The shape of the probe tip is calculated to determine the quality of the probe. The optical glass surface fabricated by free abrasive polishing (traditional mechanical polishing) technique is used as a new tip characteriser to calibrate the AFM probe tip. Meanwhile, an improved blind reconstruction algorithm is adopted to calculate the AFM tip shape and size. In the help of matrices, the blind reconstruction algorithm is elaborated clearly. The optical glass surface with irregular nanostructures ensures that the morphology of probe tip can be determined accurately. Without independent knowledge of the sample morphology, the three-dimensional morphology of the AFM tip can be obtained.

The optimum condition selection of electrochemical polishing and surface analysis of the stainless steel 316L by the Taguchi method

A development of smart materials has become a prominent issue on present industries. A smart material, included in functions, is needed for microfabrication. Complex design is able to become simply and reduce weight of parts as functionalized materials. In the traditional mechanical polishing method, even though surface roughness is good after polishing, there still remains very slight polish mark and deformed layer. Therefore, such method is not applicable to the product which requires ultra-clean surface quality. Thus, it has introduced electrochemical polishing method that electrochemical elution is applied, excluding the traditional processing method that contact between tool and workpiece always happens. In the study, Taguchi design method was introduced. By applying Taguchi design, one can significantly reduce the time required for experimental investigation, as it is effective in investigating the effects of multiple factors on performance as well as to study the influence of individual factors to determine which factor has more influence, which less. Experimental results, increases the processing time in the case of electrochemical polishing Stainless steel 316L plates were able to confirm that the improved surface quality. Start cutting after 120 s elapsed when rapidly improved surface quality showed that of the 120 s that exceeded in one area, the surface quality of the degree of improvement is slowing.

Investigation of Removal Mechanism of Sapphire in Plasma Assisted Polishing

Single crystal sapphire is widely used as the material for precision equipments, due to its high hardness, chemical inertness and light transmission. However, it is difficult to obtain a scratch-free and damage-free sapphire surface with high-efficiency through traditional mechanical polishing or etching. We developed plasma assisted polishing (PAP) for the finishing of difficult-to-machine materials, such as silicon carbide, diamond, and sapphire. In this article, preliminary research results are showed about PAP applied to polishing of single crystal c-plane sapphire substrates. Combination of helium based atmospheric pressure water vapor plasma irradiation and silica abrasive polishing drastically increased removal rate of the sapphire c-plane. XPS measurements of the surfaces with and without irradiation of water vapor plasma revealed that alumina hydrate was formed by plasma irradiation at low temperature of less than 40°C. It is assumed that formation of alumina hydrate promoted the removal rate of sapphire.

Study of Form Control Algorithm in Atmospheric Pressure Plasma Processing

Atmospheric Pressure Plasma Processing (APPP) has demonstrated that it can achieve high removal rate and induce no sub-surface damage on the silica based material of optical surface. Compared with traditional mechanical polishing and ion beam figuring, APPP technology is cost effective and very promising in the optics fabrication field. In principle, Atmospheric Pressure Plasma Processing can be described by the two-dimensional convolution equation with dwell time function and plasma removal function. Thus, dwell time function can be solved theoretically by the process of de-convolution, which is the essence of form control algorithm. First, this paper compares and analyzes common de-convolution algorithms by the simulated processing. From the simulation results, the algorithm based on the principle of image restoration has good solving speed, high calculation accuracy. Therefore, we choose it as the form control algorithm for Atmospheric Pressure Plasma Processing. However, the high temperature of plasma plume results in the non-linear relationship between the removal depth and time, further affecting the stability of the algorithm. Then, using the actual experiment data, we build the nonlinear relationship function model to compensate the heat effect in the algorithm. Finally, the modified algorithm is verified by the 7um uniform removal on the fused silica using Atmospheric Pressure Plasma Processing.

The Design of an Atmospheric Pressure Plasma Torch Used for Polishing Ultra-Smooth Surfaces

As there are always certain defects on the final surface of large-scale lightweight mirrors, which are formed in traditional mechanical polishing process, such as microcracks, lattice disturbances, plastic deformation, and so on, an atmospheric pressure plasma polishing method is a good solution to this problem. As a key component, the design of the capacitance coupling atmospheric pressure radio-frequency plasma torch is introduced. The designed torch uses water cooled coaxial aluminium electrodes with special treatment to avoid arcing between them. In normal machining process, the mixture of reaction gas and plasma gas with optimum ratio is input into the plasma torch. Then, excited by radio-frequency power, reaction gas is ionized in the plasma so as to create high density and energy reactive radicals under atmospheric pressure. The radicals cause chemical reactions with the atoms on the part surface, which performs an effective atomscale removal process. As the machining process is chemical in nature, this method avoids surface/subsurface defects mentioned above. Furthermore, initial experiment data analysis has proved that the atmospheric pressure plasma polishing method is effective and reliable, as well as demonstrates the validity of the designed plasma torch.

Structure, Impurity Composition, and Photoluminescence of Mechanically Polished Layers of Single-Crystal Silicon

The introduction of optically active defects (such as atomic clusters, dislocations, precipitates) into a silicon single crystal using irradiation, plastic deformation, or heat treatment has been considered a possible approach to the design of silicon-based light-emitting structures in the near infrared region. Defects were introduced into silicon plates by traditional mechanical polishing. The changes in the defect structure and the impurity composition of damaged silicon layers during thermal annealing (TA) of a crystal were examined using transmission electronic microscopy and x-ray fluorescence. Optical properties of the defects were studied at 77 K using photoluminescence (PL) in the near infrared region. It has been shown that the defects generated by mechanical polishing transform into dislocations and dislocation loops and that SiO2 precipitates also form as a result of annealing at temperatures of 850 to 1000°C. Depending on the annealing temperature, either oxide precipitates or dislocations decorated by copper atoms, which are gettered from the crystal bulk, make the predominant contribution to PL spectra.