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Considering the relatively poor surface and subsurface quality of workpieces that are ground by coarse-grained grinding wheels, the nanosecond ultraviolet laser micro-structuring of coarse-grained diamond grinding wheels and the grinding performance of micro-structured grinding wheels were investigated in this study. In addition, the effect of two processing sequences on the topographical characteristics of the grooves and the effect of the groove angle ( α) on the surface roughness ( R ) of the ground workpiece were explored. Furthermore, the surface quality of workpieces that were ground by micro-structured (V-shaped and W-shaped patterns) and non-structured diamond grinding wheels and the grinding ratio ( G) of the grinding wheels were comparatively analyzed. The results demonstrate the following: Compared with the grinding wheel that was subjected to micro-structuring followed by sharpening, the surface of the grinding wheel that was subjected to sharpening followed by micro-structuring had a more integral groove structure. Neither an overly large α nor an overly small α was favorable for improving the surface quality of the workpiece that was ground by a micro-structured grinding wheel. When α = 60°, the minimum R of the workpiece was attained. The R of the workpieces that were ground by the grinding wheel with a V-shaped pattern (grinding wheel A) was 17-31% less than the R of the workpieces that were ground by the non-structured grinding wheel (grinding wheel C). The R of the workpieces that were ground by the grinding wheel with a W-shaped pattern (grinding wheel B) was 32-41% less than the R of the workpieces that were ground by grinding wheel C. The grinding performance of the micro-structured grinding wheels was related not only to the geometric parameters of the grooves but also to the micro-structure pattern. The W-shaped pattern was superior to the V-shaped pattern in terms of cooling and chip removal. Grinding wheel A and grinding wheel B had similar abrasion resistance, which were 26% less and 23% less than the abrasion resistance of grinding wheel C, respectively. [ABSTRACT FROM AUTHOR]

To realize the damage-free finishing of CVD-SiC substrates, which are used as materials for space telescope mirrors and glass lens molds, plasma chemical vaporization machining (PCVM) and plasma-assisted polishing (PAP) were combined. In this study, the properties of such CVD-SiC substrates, including their surface morphology, composition and crystalline orientation, were investigated. Lapping using diamond abrasives and conventional chemical mechanical polishing (CMP) using CeO 2 slurry were conducted for comparison with the proposed atmospheric-pressure-plasma-based finishing process. Many scratches and a subsurface damage (SSD) layer were formed by the diamond lapping of CVD-SiC. Conventional CMP using CeO 2 slurry was conducted for the damage-free finishing of CVD-SiC. However, the polishing efficiency was very low. In the proposed process, PCVM, which is a noncontact dry etching process, was performed to remove the SSD layer while PAP, which combines plasma modification and soft abrasive polishing, was performed for damage-free surface finishing. PCVM was conducted on a diamond-lapped CVD-SiC surface. After PCVM for a short duration of 5 min, the scratches and SSD layer formed by lapping were completely removed, although the surface roughness was slightly increased. PAP using a resin-bonded CeO 2 grindstone was conducted to decrease the surface roughness of CVD-SiC processed by diamond lapping and PCVM for 5 min, for which a loose-held-type grindstone was demonstrated to be very useful. A flat and scratch-free surface with an rms roughness of 0.6 nm was obtained after PAP finishing. [ABSTRACT FROM AUTHOR]

Coarse-grained bronze-bonded diamond grinding wheels dressed using lasers and silicon carbide dressing wheels were used to grind YG8-cemented carbide workpieces. The wear patterns and grinding ratios of the laser-dressed grinding wheels were investigated after different grinding stages. After grinding, the laser-dressed grinding wheel displayed superior surface topography compared to the silicon carbide wheel, and the surface quality of the workpiece also improved. The minimum surface roughness of the workpiece was 0.425 μm. In the initial wear regime, the primary mechanisms included abrasive wear and grain removal. The grinding ratio was approximately 205.4, and the surface roughness of the workpiece after grinding was 0.314 μm. In the steady-state wear regime, abrasive wear was the primary mechanism of wearing, while minor amounts of grain removal and bond wear were observed. The grinding ratio was approximately 405.1, and the surface roughness was 0.337 μm. In the accelerated wear regime, the primary mechanisms were grain removal, abrasive wear, and bond wear. The grinding ratio was approximately 96.0, and the surface roughness was 0.454 μm. [ABSTRACT FROM AUTHOR]

To investigate the interaction between a laser beam and the bronze substrate in pulsed laser dressing of bronze-bonded diamond abrasive grinding wheels, a two-dimensional, transient numerical model of the three-phase (solid–liquid–gas) coupling in single-pulse laser ablation of the bronze was developed. The model accounts for the heat transfer, solidification, melting and vaporisation processes; the latent heat mechanism of the phase changes; and various critical factors such as surface tension, the vaporisation-induced recoil force, the thermal buoyancy force, and Darcy friction. The phase-field method is used to accurately track the development of the liquid/vapour (L/V) interface in the ablation crater. The finite element analysis software COMSOL Multiphysics was used to calculate the internal temperature field of the bronze substrate, the velocity field in the metallic vapour zone, and the evolution of the shape of the ablation crater during single-pulse laser ablation with various average laser power levels. The maximum error between the experimental results and the numerical analysis was less than 5%, which shows that the results are consistent. This model can accurately simulate the dynamic behaviour of the crater L/V interface during single-pulse laser ablation. This study provides a theoretical foundation for further research on laser dressing technology for bronze-bonded diamond grinding wheels. [ABSTRACT FROM AUTHOR]

For the finishing of some difficult-to-machine materials, such as silicon carbide, diamond, and so on, a novel polishing technique named plasma-assisted polishing (PAP) was proposed, which combined with the irradiation of atmospheric pressure water vapor plasma and polishing using soft abrasives. In this article, application of PAP to 4H-SiC (0001) substrate was conducted. We used helium-based water vapor plasma to modify the mechanical and chemical properties of the SiC surface. The results of X-ray photoelectron spectroscopy measurements indicate that the surface was efficiently oxidized after plasma irradiation, and the main product was SiO. CeO was used as the abrasive material in PAP, the hardness of which was near to that of the oxidized surface. The scanning white light interferometer images of the PAP processed surface showed us that scratches disappeared and surface roughness also decreased from 4.410 nm p-v, 0.621 nm root mean square (rms) to 1.889 nm p-v, 0.280 nm rms. From the atomic force microscopy images, step and terrace structure was observed on the surface after PAP, which means an atomically flat surface was obtained. The PAP processed surface was observed using cross-sectional transmission electron microscope, which indicated that almost no crystallographical defects were introduced. [ABSTRACT FROM AUTHOR]

Thermal oxidation (TO) and abrasive polishing were combined for atomic-scale planarization of 4H-SiC. It was found that the oxide/SiC interface was atomically flat regardless of the thickness of the oxide. The specimen prepared by TO was dipped in HF solution to remove the oxide. However, owing to the residual silicon oxycarbide (Si-C-O), the step/terrace structure of 4H-SiC could not be observed. Nanoindentation tests revealed that the hardness of Si-C-O was much lower than that of SiC. A thermally oxidized SiC surface was polished using CeO2 abrasives, which resulted in an atomically flat surface with a well-ordered two-bilayer step/terrace structure. [ABSTRACT FROM AUTHOR]

• Electrochemical etching-enhanced CMP is proposed for efficient polishing of GaN. • Identical-site observation was conducted to study the etching behaviors of GaN. • A maximum etching rate of 1.462 μm/min has been achieved. • Sa roughness of a dia-lapped GaN surface has been reduced from 69.8 nm to 0.64 nm. An electrochemical etching-enhanced CMP process was proposed to realize the highly efficient and damage-free finishing of GaN. In this process, electrochemical etching was first used to remove the damaged layer induced by grinding or lapping, and CMP was then conducted to flatten the etched surface. The etching rate could reach 1.46 μm/min using NaOH solution as the electrolyte which was highly efficient. It was found that the etching rate and surface roughness can be balanced by adjusting the applied potential. CMP was carried out on an etched GaN sample and the surface roughness was reduced from 69.8 nm to 0.64 nm, and its surface quality was also confirmed to be desirable through photoluminescence. These results demonstrate that the proposed electrochemical etching-enhanced CMP process is highly effective and efficient to obtain a crack-free, damage-free and smooth GaN surface. [ABSTRACT FROM AUTHOR]

The surface atomic step-terrace structure of 4H-SiC greatly affects its performance in power device applications. On the basis of the crystal structure of 4H-SiC, we propose the generation mechanism of the a-b-a*-b* type, a-b type and a-a type step-terrace structures. We demonstrate that the step-terrace structure of SiC can be controlled by adjusting the balance between chemical modification and physical removal in CeO2 slurry polishing. When chemical modification plays the main role in the polishing of SiC, the a-b-a*-b* type step-terrace structure can be generated. When the roles of physical removal and chemical modification have similar importance, the a-b-a*-b* type step-terrace structure changes to the a-b type. When physical removal is dominant, the uniform a-a type step-terrace structure can be generated. [ABSTRACT FROM AUTHOR]

Electrochemical polishing (ECP) is widely used for scratch- and damage-free finishing of metal components. Though the polishing effect of ECP has been confirmed in many researches, the influence of polishing parameters on evolution of surface roughness is still ambiguous owing to the use of different ECP systems. In this paper, the universal factor determining the evolution of surface roughness during ECP is studied by theoretical analysis as well as experiments. Theoretical analysis based on viscous layer mechanism demonstrates that the material removal thickness is the key parameter governing the roughness evolution of the polished surface regardless of other parameters including the voltage and current and electrolyte concentration. A series of experiments were designed and carried out to verify the proposed hypothesis. Both the experimental results and already published researches proved the validity and universality of the newly developed hypothesis on surface roughness evolution. This work is of great significance for further understanding the finishing mechanism of ECP and process control for its practical applications. [ABSTRACT FROM AUTHOR]

Diamond is an imperative material for fabricating functional components used in ultra-hard cutting tools, infrared optical windows, high-performance heat dissipations, and other fields. However, high surface roughness caused by competitive crystal growth in diamonds is troublesome. Besides, diamond polishing is challenging due to extreme hardness and chemical inertness. This work is focused on highly efficient and damage-free diamond polishing enhanced by atmospheric pressure inductively coupled plasma (ICP) modified silicon plate. A rapid decrease in the surface roughness from S a 308 nm–0.86 nm over 300 μm2 in 120 min proclaims ICP enhanced polishing a highly efficient technique. Simultaneously, an atomically smooth, high-quality diamond surface is obtained with a surface roughness of R a 0.26 nm over 20 μm2. The polishing mechanism based on the OH∗ modification of silicon plate and diamond surface, dehydration condensation reaction occurring at the interface of OH∗ terminated surfaces, and subsequent mechanical shearing of carbon, is proposed. The optical emission spectra of ICP, and XPS of the polished diamond surface endorse the material removal mechanism. The TEM and Raman analysis of the ICP enhanced polished surfaces promote the damage-free removal of the mechanically induced damaged layer. The ICP enhanced polishing with modified silicon plate shows great potential in damage-free atomic processing and a promising future as a commercial diamond polishing technique. [Display omitted] [ABSTRACT FROM AUTHOR]

For the highly efficient and versatile polishing of metals, isotropic etching polishing (IEP), which is based on the merging of isotropic etching holes, has been developed. In this study, the feasibility and mechanism of isotropic etching polishing of nickel-based superalloy Inconel 718 (IN718) and the polishing characteristics have been studied. The potentiodynamic experiments revealed similar trends of the cathodic, passive, second passivation, and transpassive regions in all the electrolytes, while the corrosion susceptibility of IN718 successively decreased with the increasing H 2 SO 4 concentration in the electrolyte. The etching anisotropy of the IN718 precipitated with different phases can be experimentally transmuted to isotropic etching by modulating the electrolyte concentration and keeping electrolyte temperature equal or above the room temperature. Because of the positive correlation of the etching current with isotropic holes density and diameter, etching at higher currents is promoted for the rapid and proficient polishing. The surface evolution mechanism during IEP has been confirmed. The surface roughness initially increased due to the formation of etching holes, then decreased abruptly owing to the rapid merging of etching holes and finally achieved a smooth surface. The wet grounded surface of IN718 with a roughness of Sa 62.7 nm has been transformed into a mirror-like smooth surface with a roughness of Sa 0.86 nm within 300 s of IEP at optimized conditions and a high MRR of 2.73 mm3/min has been achieved. • Electrochemical-based isotropic etching polishing mechanism of Inconel 718. • Electrolyte concentration and temperature control etching anisotropy of Inconel 718. • Two phase Inconel 718 with MC carbides was polished by isotropic etching polishing. • Inconel 718 surface roughness first increased and then decreased during polishing. • Isotropic etching polishing achieved mirror-like shining Inconel 718 surface. [ABSTRACT FROM AUTHOR]

[Display omitted] • Atomic scale smoothing of GaN is realized by plasma-based atom-selective etching. • Temperature is a key factor in determining the PASE etching mode of GaN. • Sa roughness can be reduced from 135.8 nm to 0.527 nm by 2 min of PASE. • PASE demonstrates an extremely high MRR of 93.01 μm/min. Plasma-based atom-selective etching (PASE) of GaN is conducted to realize the highly efficient planarization of the GaN surface. Inductively coupled plasma with high temperature and high concentration of radicals is used as the source of PASE. The non-toxic carbon tetrafluoride is chosen over chlorine as the reaction gas, and the volatility of the etching products will be improved at high temperatures in the PASE of GaN. After 2 min of PASE, the GaN surface roughness is reduced from Sa 135.8 nm to Sa 0.527 nm. The material removal rate of PASE of GaN is measured to be 93.01 μm/min, thousands of times higher than that of the conventional chemical mechanical polishing method. The crystal structure of the GaN subsurface is well-ordered without any damage or defects. PASE is thus proven to be a non-destructive etching method. In this study, the effects of radio frequency power and reaction gas flow rate on PASE are also investigated. Surface temperature and concentration of radicals are found to be the critical factors in the PASE of GaN. [ABSTRACT FROM AUTHOR]

Microfluidic chips made of glass are important analytical devices for applications in biomedicine, drug development and chemical analysis. For the mass production of glass-based microfluidic chips, tungsten-made microfluidic moulds are indispensable. In this paper, a dynamic electrochemical polishing (ECP) process using a bi-layer NaOH electrolyte is proposed to uniformly polish tungsten moulds. The ECP conditions are optimized to determine the best anode potential and polishing duration. The problem of pitting during ECP can be solved by an ultra-short ECP post-treatment of several seconds. During static ECP, the material removal on the mould is nonuniform, and material removal uniformity is greatly improved by dynamic ECP. After 10 cycles of dynamic ECP, a tungsten mould with a mirror surface is obtained, and the surface roughness (Sa) is drastically reduced from 205.98 nm to 4.14 nm. The results presented in this paper demonstrate that dynamic ECP is a promising approach for highly efficient and uniform polishing of tungsten moulds with microscopic features. [ABSTRACT FROM AUTHOR]

To realize the damage-free, highly efficient, and atomic-level polishing of single-crystal Si, plasma-based atom-selective etching (PASE) is proposed in this study as a generic polishing approach for Si wafers. The polishing effect of PASE is realized through the selective removal of Si atoms with more dangling bonds under high temperature. Plasma diagnostics are carried out to investigate the radical composition, the density of plasma, and the etching temperature. The key parameters of PASE are optimized, and the PASE of Si (100) with a material removal rate greater than 0.7 μm/min was realized. A ground Si (100) surface can be quickly smoothed by PASE, with the Sa roughness being reduced from 195 nm to below 1.0 nm within 5 min, and the polished surface is proven to be crystallographically perfect. The PASE of (110)- and (111)-oriented Si wafers is also proven effective, demonstrating that PASE is a generic polishing approach for Si regardless of orientation. The entire surface flattening of a 2-inch Si wafer was carried out by numerically controlled PASE, and the wafer flatness was reduced from 37.29 μm to 4.92 μm through optimized scanning conditions. Overall, this study has shown that PASE is a promising approach for high-efficiency and high-quality polishing of Si. Image 1 • Plasma-based atom-selective etching (PASE) was proposed as a Si polishing technique. • Inductively coupled plasma with high radical density and high temperature was utilized. • Sa roughness of Si was reduced from 195 to 0.71 nm with a maximum MRR of 0.7 μm/min. • Temperature played a key role in PASE to determine the polishing effect. • PASE was effective for (100)-, (110)-, and (111)-oriented Si wafers. [ABSTRACT FROM AUTHOR]

• Molten KOH etching have been first applied to polishing sliced SiC. • Sa roughness is reduced from 246.5 nm to 16.06 nm within 2 min of molten KOH etching. • A damage-free surface can be obtained. • Etching behaviors and mechanisms for dislocation spot is particularly studied. Single-crystal silicon carbide (4H-SiC) is a promising third-generation semiconductor material because of its excellent electrical, mechanical and chemical properties. However, the high hardness of 4H-SiC makes it a typical difficult-to-machine material, which greatly restricts the development of SiC devices. In this work, molten KOH etching was first used to polish SiC. The perfect crystal surface and dislocation spots were studied separately. For the perfect crystal surface, a typical isotropic etching polishing behavior was observed. The speed of the polishing process was closely correlated with the temperature. An ultrafast polishing of sliced SiC was achieved, reducing the roughness from 246.5 nm to 16.06 nm within 2 min at 800 °C, and all subsurface damage was removed, as demonstrated by TEM. For the dislocation spot, a relationship between the etch pits angle and temperature was found, making it possible to remove the influence of the dislocation spot by increasing the etch pits angle to approach 180°. This study shows that molten KOH etching could be a very promising SiC polishing method and deserves further research. We anticipate that this approach will be applicable to ultrafast polishing of SiC at the industrial scale. [ABSTRACT FROM AUTHOR]