金刚石与磨料磨具工程

Key factors affecting the performance of diamond wire drawing die coatings

, Available online , doi: 10.13394/j.cnki.jgszz.2024.0104

Abstract(426)

Abstract:
Abstract： Diamond has high hardness, elastic modulus and other properties, irreplaceable role in the tool market, for the relevant enterprises to bring stable earnings.The diamond wire drawing die is extensively employed in the metal drawing and strand tightening fields, primarily due to its remarkable hardness. This attribute enables the die to withstand the immense pressures and friction encountered during the drawing process, ensuring that the wires are pulled through with precision and minimal resistance. The high hardness of the diamond not only facilitates the reduction of the wire diameter but also contributes to the integrity and strength of the finished product. The metal drawing properties of diamond coating are closely related to the microstructure.
【Objectives】In this research, the selection of two pivotal temperature 900℃ and 950℃, was based on extensive prior experimentation. These temperatures were chosen for their significant impact on the material's properties and the outcomes of the processes. The effect of the two processes on microstructure and the difference of failure mechanism were studied.
【Methods】Based on the simulation method, the temperature distribution in the drawing die is analyzed, Scanning Electron Microscopy (SEM) is employed to observe the surface topography of diamond drawing die at high magnification. X-ray Diffraction (XRD) analysis is then conducted to investigate the crystallographic structure of the diamond drawing die. Additionally, Raman spectroscopy is used to analyze quality of the diamond drawing die.
【Results】The results show that the temperature gradient inside the die is small so the direct effect of temperature on diamond coating deposition is small. High temperature can promote carbon active groups to enter the compression and sizing regions to form nanodiamonds, while lower temperature will weaken the diffusion ability of carbon active groups and form micrometer diamonds in the compression and sizing regions. Nanometer diamond coating has good performance, but weak binding force leads to the failure of large diamond coating. Micrometer diamond film hardness is higher, surface roughness control is difficult, will lead to a coarse metal surface.
【Conclusions】Based on this analysis, a method of in-situ deposition of nanometer diamond coating on micron diamond coating is proposed in this study, which can effectively improve the service life of wire drawing die, the wire drawing distance can be increased to more than 100km.

Study on diamond bimetallic coating technology

, Available online , doi: 10.13394/j.cnki.jgszz.2024.0098

Abstract(604)

Abstract:
Objectives:
In order to optimize the performance of diamond and improve its utilization rate, this paper carried out metallization treatment on the surface of diamond and successfully achieved reliable control of coating thickness.

Methods:
This article uses a high-temperature molten salt plating method to uniformly coat the surface of diamond with 1-5 μ m titanium nickel, titanium molybdenum, titanium tungsten, and titanium cobalt bimetallic coatings. In order to deeply analyze the composition and morphology characteristics of bimetallic coatings on diamond surfaces, advanced characterization techniques such as XRD (X-ray diffraction), EDS (energy dispersive spectroscopy), XPS (X-ray photoelectron spectroscopy) were used to comprehensively characterize and analyze the composition of the coatings. At the same time, SEM (scanning electron microscopy) was used to observe the morphology of the coatings in detail. In addition, Nano Measure and AFM (atomic force microscopy) were used to measure the thickness and surface roughness of four different diamond coatings.

Results:
The experimental data results show that under the conditions of coating temperature of 1000 ℃ and insulation time of 60 minutes, all four diamond bimetallic coatings can form titanium carbide coatings and titanium coatings, and stable compounds are formed between nickel, molybdenum, tungsten, cobalt elements and titanium. The presence of these compounds in the diamond coating forms stable chemical bonding energy, ensuring the stability and reliability of the coating. The titanium nickel, titanium molybdenum, titanium tungsten, and titanium cobalt bimetallic coatings on the surface of diamond particles are uniform and dense. The coating thickness of the four diamond bimetallic coatings is strictly controlled within the range of 1-5 μ m. Effective control of diamond coating thickness provides the possibility for achieving efficient application of diamond tools in various environments. Further research has found that among the four diamond bimetallic coatings, the roughness of the diamond (100) crystal plane is generally greater than that of its (111) crystal plane. Specifically, among the four types of diamond bimetallic coatings, the diamond titanium cobalt bimetallic coating exhibits the highest surface roughness and thinnest coating thickness, which is closely related to the differences in affinity and mismatch between metal nickel powder, molybdenum powder, tungsten powder, cobalt powder, diamond, and titanium powder during the salt bath plating process. Due to the high affinity between titanium powder and diamond, it preferentially reacts with diamond to generate TiC. This type of carbide not only improves the wettability of nickel, molybdenum, tungsten, cobalt and diamond, but also enhances the bonding force between diamond and metal matrix, making the bimetallic coating on the surface of diamond more uniform and dense.

Conclusions:
The metallization coating treatment on the surface of diamond not only provides effective protection for diamond, but also significantly increases the oxidation temperature of diamond. Meanwhile, due to the controllability of diamond coating thickness, this technology is expected to further expand the application range of diamond tools and meet more complex and demanding working environment requirements. This research achievement is of great significance for improving the performance and service life of diamond tools, and provides strong technical support for the widespread application of diamond materials.

Experimental Study on Magnetic Abrasive Finishing of Inner Pipe Surface Based on Optimized Halbach Array

, Available online , doi: 10.13394/j.cnki.jgszz.2024.0092

Abstract(406)

Abstract:
Objectives:To address the issue of low magnetic induction intensity and insufficient renewal of magnetic abrasive particles in magnetic abrasive finishing (MAF) of pipes, which results in low inner surface machining efficiency.

Methods:This paper proposes a novel method to enhance the finishing process. This method utilizes an optimized Bilateral Halbach array magnetic pole structure to improve the magnetic induction intensity and gradient within a confined space. Firstly, finite element software was used to analyze the magnetic field distribution of various magnetic pole structures. The Bilateral Halbach array magnetic poles were found to produce a stronger single-peak magnetic field in the machining area compared to other magnetic pole structures. Secondly, theoretical and simulation models were employed to identify the auxiliary magnetic pole height and thickness as sensitive parameters affecting the magnetic induction intensity and gradient of the Halbach array magnetic poles. These parameters were then used as optimization variables. Neural networks were utilized to fit the predictive model, ensuring accurate representation of the relationship between these parameters and the resulting magnetic field characteristics. The Non-dominated Sorting Genetic Algorithm Ⅱ (NSGA-Ⅱ) was applied to the predictive model to seek the Pareto optimal solution set, thereby determining the optimal configuration of the Halbach array. The use of NSGA-Ⅱ allowed for the simultaneous optimization of multiple objectives, ensuring that the final design provided a balance between high magnetic induction intensity and gradient. This optimal configuration, combined with the radial reciprocating feed of the magnetic poles, aimed to increase grinding pressure while simultaneously enhancing the turnover and renewal of the magnetic abrasive particles. Finally, the performance of different magnetic pole structures at two different rotational speeds was validated through simulations and experimental tests. The magnetic abrasive particle dynamics were simulated to provide insights into their behavior under varying conditions, while experimental tests confirmed the practical applicability of the theoretical and simulation findings.

Results:Experimental validation demonstrated that the optimized Bilateral Halbach array magnetic poles effectively increased magnetic induction intensity and gradient. Compared to the traditional N-S pole structure, the maximum magnetic induction intensity increased by 60%, and the magnetic field gradient improved by -30 mT/mm. The magnetic brush within the pipe exhibited stronger agglomeration strength, leading to higher processing efficiency. After 30 minutes of processing, the inner surface roughness of the pipe decreased to Ra 0.068 μm. The inner surface's oxide layer and original defects were completely removed, leaving only uniform transverse machining marks. The efficiency of the MAF process was improved by 90%.

Conclusions:The MAF process efficiency was improved by 90%, demonstrating the substantial benefits of the optimized Halbach array. The higher grinding pressure and more frequent turnover of the magnetic abrasive particles led to faster and more effective material removal, enhancing the overall efficiency of the finishing process. The optimized Bilateral Halbach array magnetic pole structure effectively enhanced the magnetic induction intensity and gradient within the pipe, leading to significant improvements in the efficiency and quality of the MAF process. During the finishing process, the magnetic brush inside the pipe exhibited high agglomeration strength, reducing the loss of magnetic abrasive particles and increasing grinding pressure. The frequent turnover and renewal of the magnetic abrasive particles extended their lifespan, ensuring consistent grinding efficiency and achieving a high-quality surface finish.

Surface morphology segmentation and evaluation of diamond lapping pad based on improved Mask R-CNN

, Available online , doi: 10.13394/j.cnki.jgszz.2024.0080

Abstract(495)

Abstract:
Objectives:Diamond lapping pads have significant characteristics such as fast cutting speed, high machining accuracy, wide application range, and certain self-sharpening. They are widely used in the grinding of various hard and brittle materials. However, during processing, the lapping pad is prone to wear, and the surface morphology changes after wear. Its surface morphology has a direct impact on the quality of the workpiece and the lapping performance of the lapping pad. This article explores the use of deep learning methods to accurately and efficiently detect the surface morphology of the lapping pad, and evaluates the effectiveness of the detection method.

Methods:An improved Mask R-CNN model segmentation method is proposed based on the characteristic of improving perceptual field of view through dilated convolution, which identifies and segments the diamond abrasives and pores in the surface images of the lapping pad. The model is trained and verified using a dataset of diamond lapping pads with magnesium oxychloride binder after grinding sapphire; In order to verify the difference between the diamond abrasives and pores segmented using this method and the actual results, three parameters of target number recognition accuracy, target segmentation area accuracy and target position error are proposed to evaluate the segmentation effect.

Results:Through training and verification of the improved Mask R-CNN segmentation model, the results show that this method can realize the recognition and segmentation of diamond abrasives and pores in the surface images of the lapping pad, and the average accuracy is 78.2 %. By comparing the segmentation results of the model with the manually annotated results, and calculating the three segmentation evaluation parameters, the results show that the number of diamond abrasives and pores obtained by the improved Mask R-CNN model recognition segmentation method does not differ significantly from the actual number of diamond abrasives and pores. However, due to the complex background of the surface image of the lapping pads and the unclear contrast between abrasive particles, pores and binder, there are certain missed or false detections when using this method to detect the surface morphology of the lapping pads, the recognition accuracy of the number of diamond abrasives and pores is 82.1 % and 93.4 %, respectively; the method has a good segmentation effect on the identified targets, with small differences between the segmented abrasive and pore areas and the actual areas, and a high degree of agreement, the segmentation area accuracy for diamond abrasives and pores is 89.9 % and 95.3 %, respectively; the contour of the diamond abrasives and pores obtained by this method is slightly different from the actual contour, but the centroid position error is small, the position error for diamond abrasives and pores is 3.8 % and 2.8 %, respectively.

Conclusions:The comparison between the improved Mask R-CNN model segmentation image and the manually annotated image, and the calculation of three evaluation parameters, fully demonstrate that the use of the improved Mask R-CNN segmentation model has a good effect on the segmentation of diamond abrasives and pores on the surface of lapping pads, proving the effectiveness of the segmentation method.

Advance on molecular dynamics simulations of precision polishing of SiC

, Available online , doi: 10.13394/j.cnki.jgszz.2024.0070

Abstract(701)

Abstract:
【Background】SiC has high hardness, brittleness, and chemical stability, making it exceptionally difficult to perform ultra-precision processing on its surface. This results in high processing costs, severely limiting the application and development of SiC in high-end devices. Chemical mechanical polishing (CMP) is a key technology for the planarization of SiC substrates. Currently, there is a large amount of research on CMP polishing processes, but the interaction mechanism between abrasives and chemicals in the solvent and the SiC surface is not clear. Molecular dynamics (MD) simulation, based on Newton's motion law and quantum mechanics principles, is a simulation method used to reveal the interaction between microstructure and properties of substances. It is widely used in the study of the removal mechanism of SiC surfaces.
【Content】The article first summarizes the current mainstream chemical mechanical polishing methods and their enhancement methods. Then, it analyzes the commonly used potential functions in MD simulations of SiC precision polishing, and summarizes their application areas in SiC chemical mechanical polishing based on the characteristics of potential functions. Finally, the existing research on MD simulation of SiC chemical mechanical polishing is integrated and analyzed, summarizing the removal behavior of abrasives on the SiC surface and the mechanism of adsorption and oxidation of solutes and solvents in the polishing liquid on the SiC surface, and prospects for future research directions in SiC chemical mechanical polishing.
【Current Status】The results indicate that mature simulation methods have been developed for mechanical behaviors in SiC CMP MD simulations, particularly in simulating abrasive-SiC surface interaction mechanisms and mechanical properties. The Tersoff potential, as the most classical description of the interaction between silicon and carbon atoms, can well describe the mechanical behavior of SiC and is used to study the mechanical properties and structural changes of SiC. The ABOP potential function is suitable for describing the atomic interactions of SiC materials.The Vashishta potential function is mainly used to simulate the deformation of 3C-SiC ionic bonds and covalent bonds. ReaxFF reactive force field, because it can support the formation and fracture of chemical bonds, is often used to study the chemical reactions and adsorption behavior of SiC surfaces. MD simulation of SiC substrate precision polishing is mainly divided into three categories: SiC material properties, abrasive grinding, and SiC surface chemical reactions. At present, most research focuses on the mechanical behavior between abrasives and SiC surfaces, with relatively few studies on chemical reaction mechanisms.
【Prospects】Currently, there are still many unclear issues in the CMP mechanism of SiC materials. Molecular dynamics simulations can be used to study the interaction mechanisms between liquids, oxides, and surfaces in chemical mechanical polishing, such as charge transfer and surface adsorption. In the future, the focus of research will be on using ReaxFF reactive force fields to study the reaction mechanisms of SiC under various conditions through molecular dynamics simulations, building more potential functions to adapt to different polishing conditions, and establishing comprehensive models considering the effects of multiple factors on surface interactions.

Effect of heat treated tungsten interlayer on microcrystalline diamond coatings

, Available online , doi: 10.13394/j.cnki.jgszz.2024.0063

Abstract(487)

Abstract:
Objectives: Microcrystalline diamond coatings have extremely high hardness and excellent wear resistance, but its application field is limited by poor tribological and binding properties. To improve the tribological properties of microcrystalline diamond coatings on cemented carbide substrates, we have chosen tungsten metal as the interlayer material and constructing microscopic texture by heat treatment on the surface of tungsten interlayer.

Methods: We used evaporation method to deposit a tungsten interlayer on the surface of cemented carbide, and heat treated the tungsten interlayer in a reducing atmosphere mixed with argon and hydrogen gas. After heat treatment for 30 minutes at various temperatures (700 / 800 / 900 / 1000 °C), the effects of different heat treatment temperatures on the composition, morphology, and microstructure of the tungsten transition layer were studied using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). Diamond coatings were deposited using hot filament chemical vapor deposition (HFCVD) method on substrates without any treatment and tungsten interlayers which were teated by different temperature. The substrate temperature was controlled at 800 ± 50 ℃, and the growth time was 6 hours. Analyze the morphology and quality of diamond coatings using SEM, X-ray diffraction, and laser Raman spectroscopy. Using the reciprocating friction and wear tester, Si₃N₄ ceramic balls were subjected to reciprocating friction with diamond coatings for 120 minutes to evaluate the friction performance of each coating sample.

Results: The results show that the tungsten interlayer deposited by vapor deposition exhibits an amorphous structure, and the crystallinity of the tungsten interlayer significantly increases after heat treatment. Cracks are generated on the surface of the interlayer, and different sizes of "island - gully" structures are formed. The crystallinity of the tungsten interlayer after heat treatment at 700~800 ℃ is not good, and the surface has larger "islands" and narrower "gully". The structure size of the tungsten interlayer after heat treatment at 900 ℃ is more moderate. The tungsten interlayer after heat treatment at 1000 ℃ has the best crystallinity and the smallest size of "islands". The SEM surface morphology, X-ray diffraction patterns, and Raman spectroscopy show that the diamond grown on the substrate surface without tungsten transition layer has the largest average grain size and uneven grain size distribution. The crystallinity and content of diamond coatings grown on the tungsten interlayer during heat treatment are better, which was reflected in the higher diffraction intensity of diamond peak in the X-ray diffraction spectrum and the narrower full width at half maximum (FWHM) of diamond peak in the Raman spectrum. The grain size of diamond shows a trend of first decreasing and then increasing with the increase of heat treatment temperature, but all are smaller than the sample without tungsten interlayer. The friction and wear results indicate that the diamond coating grown on the tungsten interlayer after 700 ℃ heat treatment has large drop. The diamond coating on the tungsten interlayer after heat treatment at 800~1000 ℃ ensures good bonding performance while improving friction performance in varying degrees. Among them, the diamond coating grown on the tungsten interlayer after 900 ℃ heat treatment has the smoothest wear mark, with an average friction coefficient as low as 0.062, and the corresponding Si₃N₄ friction pair has the smallest wear mark diameter and wear rate.

Conclusions: The tungsten interlayer and its "island - gully" structure after heat treatment can significantly improve the growth and crystal state of diamond, resulting in grain refinement and improved friction properties. The surface of the tungsten interayer treated at 900 ℃ for 30 minutes has a moderately sized "island-gully" structure and the best uniformity. The average grain size of the diamond coating grown on it is about 1.97 μm. The maximum and average friction coefficients are as low as 0.217 and 0.062, and the wear of friction pair is only 19.2% of the sample without tungsten interlayer.

Study on the performance of brazed micronized diamond grinding head

, Available online , doi: 10.13394/j.cnki.jgszz.2024.0025

Abstract(588)

Abstract:
In order to solve the problems of serious damage of micronized diamond during brazing and poor bonding between brazing material and substrate. A suitable brazing method was used to braze micronized diamond (325/400#) on a steel substrate. The bonding interface was analyzed and a grinding head was prepared to process the alumina ceramic plate. It was found that the micronized diamond abrasive grains were less damaged. The products at the interface between the steel substrate and the brazing material are γ-phase solid solution formed by Fe and Cr and Ni-Fe replacement solid solution formed by Fe and Ni. The presence of solid solution ensures a strong bond between the brazing material and the substrate. The prepared brazed micronized diamond grinding heads have a high service life when processing ceramic plates.

, Available online , doi: 10.13394/j.cnki.jgszz.2024.0019

Abstract(426)

Abstract:
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, Available online , doi: 10.13394/j.cnki.jgszz.2023.0046

Abstract(607)

Abstract:

Prediction of grinding surface roughness of Al2O3-based insulating coating on bearing surface considering the change of grinding wheel surface morphology

, Available online , doi: 10.13394/j.cnki.jgszz.2023.0118

Abstract(654)

Abstract:
To improve the prediction accuracy of grinding surface roughness of Al2O3-based ceramic insulating coating on bearing surface, a BP neural network prediction model was established which was consistent with the actual machining process. A method for measuring grinding wheel surface and quantifying abrasive particle characteristic parameters was proposed based on the principle of spectral confocal. A neural network prediction model for workpiece surface roughness was established, which took characteristic parameter K of grinding wheel surface, grinding wheel speed ω, workpiece feed speed υ, cutting depth ρ and normal grinding force F as input parameters. The model could directly reflect the time-varying state of grinding wheel surface. Finally, the prediction performance of the network was verified by the known grinding samples and the four groups of unknown test samples after grinding wheel passivation. For the known samples, the roughness predicted by BP network is consistent with the actual roughness, and the network output error is less than ±0.04μm. Further using the network for the grinding wheel after passivation to predict the unknown grinding test samples, the accuracy of the network prediction decreases, and the maximum error percentage is less than 20%. The neural network, which includes the characteristic parameters of abrasive particles on grinding wheel surface, can be used to predict the workpiece roughness of Al2O3-based ceramic insulation coating on bearing surface under the transient state of abrasive wear of grinding wheel, and the network has a certain generalization ability for unknown samples.

Effect of pad and slurry on fixed abrasive polishing of gallium oxide crystal

, Available online , doi: 10.13394/j.cnki.jgszz.2022-0043

Abstract(1204)

Abstract:
Gallium oxide crystal is the most representative fourth generation semiconductor material with the advantages of high band gap, high voltage resistance and short absorption cutoff edge, and has broad application prospects. Gallium oxide crystal is prone to micro-cracks, scratches and other surface defects in the polishing process, which is difficult to achieve high-quality surface processing and cannot meet the requirements of the corresponding devices. Moreover, the existing polishing process of gallium oxide crystal is complex and inefficient. Fixed abrasive polishing technology has the advantages of controllable abrasive distribution and depth of cut, and high utilization rate of abrasive grain. Fixed abrasive polishing was used, and the effect of pad and slurry on material removal rate and surface quality were explored in fixed abrasive polishing of gallium oxide crystal. The results show that when the hardness of the polishing pad is moderate II, the abrasive concentration is 100%, and the slurry additive is oxalic acid, material removal rate is 68 nm/min, and the surface roughness Sa value is 3.17 nm in fixed abrasive polishing gallium oxide crystal. Fixed abrasive polishing technology can achieve efficient and high-quality polishing of gallium oxide crystal

Development of CAM system for automatic compound dressing of superabrasive grinding wheels

, Available online , doi: 10.13394/j.cnki.jgszz.2022-0061

Abstract(882)

Abstract:
In the field of superabrasive wheel dressing, multi-process composite dressing has obvious advantages, but there is no research related to the automation system of grinding wheel composite dressing. In order to make the integration of multiple processes in the composite dressing method more systematic and improve the dressing efficiency of shaped grinding wheels, this paper develops a CAM system by self-developed laser-mechanical composite dressing equipment, which can, according to different grinding wheel section shapes, automatically plan the dressing trajectory under multiple processes and dressing strategies, calculate the dressing toolpath with planar three-axis linkage, automatically generate the machining code, and at the same time design a visualisation interface to simulate the machining process. The results of dressing experiments on 150# diamond bronze bonded grinding wheels show that the system can generate machining programs for laser roughing, semi-finishing and mechanical finishing without collision and overcutting of the machine tool, and significantly improve the programming efficiency of the compound dressing method. And the dressing wheel profile error is within 9.1 µm and circular runout error is 6.1 µm.

Study on the Mechanism and Process Magnetorheological Variable Gap Dynamic Pressure Planarization Finishing

, Available online , doi: 10.13394/j.cnki.jgszz.2022-0004

Abstract(923)

Abstract:
In order to improve the polishing efficiency of magnetorheological polishing and realize the high-efficiency, high-quality and ultra smooth planarization of photoelectric wafer, a magnetorheological variable gap dynamic pressure planarization method is proposed. In this paper, the changes of material removal rate and surface roughness of sapphire wafer surface polishing with processing time under different variable gap conditions are studied, and the dynamic pressure flattening mechanism of magnetorheological variable gap is deeply analyzed. The results show that the dynamic change of polishing pressure and the extrusion strengthening effect of MR fluid can be produced by applying axial low-frequency extrusion vibration to MR polishing fluid, and the polishing efficiency and polishing effect can be significantly improved. After 120 min of magnetorheological variable gap dynamic pressure flattening, the surface roughness of sapphire wafer decreased from Ra 7 nm to Ra 0.306 nm, and the material removal rate was 5.519 nm / min. Compared with constant gap magnetorheological polishing, the surface roughness decreased by 49% and the material removal rate increased by 55.1%; By changing the moving speed of variable clearance, the flow field characteristics can be controlled. Choosing the appropriate workpiece pressing speed and workpiece lifting speed is conducive to improve the polishing efficiency and surface quality.

Effect of Fe₃O₄ Characteristics on Properties of Solid-phase Fenton Reaction Lapping Pellets for Single-Crystal SiC

, Available online , doi: 10.13394/j.cnki.jgszz.2022-0008

Abstract(914)

Abstract:
To improve the lapping quality and processing efficiency of single-crystal SiC, solid-state Fenton reaction lapping pellets were prepared. Effects of particle size and concentration of Fe₃O₄solid-phase catalyst on the physical properties (hardness, flexural strength, porosity), catalytic performance, and lapping performance of single-crystal SiC were studied. The results showed that with the increase of Fe₃O₄ particle size, the hardness, flexural strength, porosity, and catalytic performance of the lapping pellets all decreased, the material removal rate (MRR) decreased from 43.12 nm/min to 36.82 nm/min, and the surface roughness (Ra) increased from 1.06 nm to 3.72 nm. As the Fe₃O₄ concentration increased, the hardness and flexural strength of the lapping pellets decreased, and the porosity and catalytic performance increased. Although the material removal rate decreased, the surface roughness (Ra) decreased firstly and then increased. The MRR decreased from 40.14 nm/min to 33.51 nm/min, the surface roughness (Ra) was 3.25 nm, 1.75 nm and 1.88 nm. In this experiment, when the Fe₃O₄ particle size and the concentration was 0.5 µm and 29 wt.%, the processing effect was the best, the MRR and the surface roughness (Ra) was 43.13 nm/min and 1.06 nm.

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