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2025, Volume 45,  Issue 3

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Advances in studies and applications of thick diamond films prepared by microwave plasma chemical vapor deposition
LIU Fucheng, MA Guanjie, HUANG Jiangtao, ZHANG Zongyan, HAN Peigang, HE Bin
2025, 45(3): 285-299. doi: 10.13394/j.cnki.jgszz.2023.0270
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  Significance  With the wide range of important applications of diamond, the demand for large-area diamond has been increasing in recent years. Compared to other chemical vapor deposition (CVD) methods, the microwave plasma chemical vapor deposition (MPCVD) method is recognized as the best technology for depositing high-quality diamond films. To realize CVD diamond thick films for optical, electrical, and thermal applications, it is necessary to meet the requirements in terms of crystalline quality, optical transmittance, thermal conductivity, size, thickness, and strength. Therefore, obtaining diamond materials with sufficient size and quality is the foundation of their applications. Especially since this century, MPCVD equipment and processes have made breakthroughs, and the preparations of single crystal diamond and high-quality polycrystalline diamond thick films have been successfully realized. This paper introduces the principles and process of preparing diamond thick films by MPCVD, and summarizes the research and application progress of MPCVD-prepared diamond films at home and abroad in recent years. Our views on the future development of MPCVD-prepared diamond films are also proposed in this paper.  Progress  The MPCVD equipment originated overseas, initially developed by Japanese scientist Yoshihiko Kuriyama and researchers from Nippon Electric Company around the 1980s. Subsequently, countries such as Germany, Britain, the United States, and Russia also engaged in research and development efforts. The evolution of MPCVD chambers has seen a transition from quartz tubes and quartz bell jars to cylindrical resonance chambers, loop antennas, and ellipsoidal resonance chambers. Concurrently, power output has escalated from hundreds of watts to thousands and tens of kilowatts. The advancement of MPCVD technology was spearheaded by foreign entities like E6 (UK), Michigan State University (USA), and the Institute of Applied Physics (Russia), which gradually increased power levels and evolved cavity designs. With progress in diamond film deposition technology and ongoing exploration of microwave sources, higher-power 915 MHz MPCVD systems have been developed. The longer wavelength of 915 MHz microwaves enables these devices to achieve higher power levels, which facilitates an increase in the deposition rate and quality of diamond films, as well as the capability to produce larger-sized diamond films. Domestic development of MPCVD technology began relatively late, with institutions such as the University of Science and Technology Beijing, Hebei Province Laser Research Institute, and Xi'an University of Electronic Science and Technology developing 2.45 GHz and 915 MHz MPCVD equipment after the year 2000. Diamonds possess a high refractive index and significant dispersion, exhibiting superior thermal, mechanical, and optical properties. High-quality polycrystalline diamond films synthesized via the MPCVD method closely resemble natural type IIa diamonds in many aspects. Consequently, MPCVD-prepared diamond films have found extensive applications in optical window materials, thermal management, semiconductor devices, quantum technology, and optoelectronic devices. The third section of the paper provides a detailed account of the progress in applied research within these areas.   Conclusions and Prospects  Diamond is a material of significant interest and extensive research in the contemporary world. Over the decades, CVD diamond technology has matured, with preparation processes becoming well-established and the equipment continuously evolving and refining. Among the various CVD techniques, MPCVD equipment has seen particularly rapid development. Through persistent exploration, research, and development, the performance gap between domestically produced 2.45 GHz and 915 MHz MPCVD equipment in China and their foreign counterparts is narrowing, although there is still room for improvement in terms of power enhancement, equipment stability, and cavity design. MPCVD-method-prepared diamond thick films hold great promise for a variety of high-tech applications, including optics, thermal management, and electronics. However, their growth rate, size, and uniformity remain areas that require further attention. Looking ahead, ongoing research is essential in several key areas: optimizing and enhancing equipment, refining the growth process, and innovating process parameters (such as atmosphere, power, and substrate) to achieve higher growth rates, superior quality, and reduced costs. These efforts aim to meet the demands of commercialization, thereby facilitating the widespread adoption of diamond thick films in thermal deposition and optical applications.
Applications of nanodiamonds in medical and sensor fields
JIANG Lin, WANG Chengyong, ZHANG Yue, GUO Ziying
2025, 45(3): 300-315. doi: 10.13394/j.cnki.jgszz.2024.0028
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  Significance  This study systematically reviews the applications of nanodiamonds in the medical and sensor industries, along with their fabrication techniques and inherent properties. Nanodiamonds, characterized by their unique physicochemical attributes, such as high hardness, favorable biocompatibility, optical characteristics, and electrical properties, are posited to hold substantial promise for diverse applications in these domains.  Progress  The article delineates a variety of synthesis methods for nanodiamonds, encompassing detonation synthesis, chemical vapor deposition, ball milling, high-temperature high-pressure synthesis, and laser ablation. It also presents an analytical review of the advantages and disadvantages inherent to each technique. Furthermore, the study addresses advancements in nanodiamond surface modification, biocompatibility, and electrical and optical properties. It concludes with a comprehensive summary of nanodiamond applications in the medical and sensor fields, highlighting their utilization in biological labeling and imaging, anti-infective therapy, tissue engineering and repair, cancer treatment, biosensors, electrochemical and gas sensors, and pressure sensors, among others.  Conclusions and Prospects  The article acknowledges the broad application prospects of nanodiamonds in the medical and sensor sectors, while also highlighting existing research gaps, such as the need for improved purity, yield, and size uniformity during synthesis, challenges in achieving efficient and controllable fluorescence for imaging, and an incomplete understanding of nanodiamonds' metabolic pathways and biological impact within living organisms. The article also speculates on potential future directions for nanodiamond research, including enhancing synthesis quality, achieving precise control over fluorescence properties, elucidating their metabolic pathways and biological effects, and developing more efficient and sensitive biosensors. This review article offers a comprehensive research perspective on the applications of nanodiamonds in the medical and sensor fields, and presents constructive suggestions for future research directions.
Effect of diamond content on properties of Ni-Cu/diamond composites prepared by electron beam selective melting
LI Haodong, WANG Haishan, FAN Yonggang
2025, 45(3): 316-324. doi: 10.13394/j.cnki.jgszz.2024.0079
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  Objectives  Polycrystalline diamond composite (PDC) drill bits are formed by sintering or inlaying polycrystalline diamond composite into the matrix of the drill bits, and are widely used in the engineering field due to their excellent performance. Compared with steel-body PDC bits, matrix-body PDC bits have superior abrasion resistance and erosion resistance. However, under extremely severe working conditions, the matrix-body PDC drill body material still faces challenges in practical applications, and the preparation process of the drill matrix material is complicated and cumbersome. Therefore, it has become an inevitable trend to prepare drill matrix materials with excellent performance through more efficient preparation methods.   Methods  Ni-Cu/diamond composites, as potential PDC drill bit matrix, are successfully prepared by electron beam selective melting (EBSM). The effects of diamond content on the wear resistance and erosion resistance of Ni-Cu/diamond composites changes are systematically investigated.  Results  The results show that the wear ratio of the specimens first increases and then decreases as the volume fraction of diamond increases from 10% to 35%, while the erosion resistance shows an opposite trend. When the volume fraction of diamond is below 25%, the lower content of diamond is sparsely distributed in the metal matrix. At this time, the advantages of its high hardness contribute less to the overall abrasion resistance and erosion resistance of the composite specimens, with the metal matrix occupying the main position. In this diamond content range, the wear ratio of the sample is relatively small but increases with the increase of diamond content, while the weight loss after the erosion test is large but decreases with the increase of diamond content. When the volume fraction of diamond reaches 25%, the diamond particles are uniformly distributed in the metal matrix and tightly bonded to it, significantly enhancing the wear and erosion resistance of the sample. Meanwhile, the wear ratio reaches the maximum value of 1.09, while the weight loss after the erosion test reaches the minimum value of 7.15 mg. However, when the volume fraction of diamond increases to 30% and 35%, excessive diamond particles in the matrix exhibit large-scale agglomeration and direct connection. Due to the loss of the metal matrix's ability to bind and hold them, the diamond particles fall off in clumps during wear and erosion tests, resulting in a significant decrease in wear resistance and erosion resistance of the specimens.   Conclusions  The wear resistance and erosion resistance of PDC bit matrix materials are key factors determining the overall performance of PDC bits, as expressed by the above wear rate and weight loss after erosion tests. Therefore, it can be concluded that when the diamond volume fraction is 25%, the overall wear resistance of the Ni-Cu/diamond composite material reaches its best level.
Research on current situation and development trends of China’s lab-grown diamond market
ZHANG Dong
2025, 45(3): 325-331. doi: 10.13394/j.cnki.jgszz.2023.0263
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  Significance   Since natural diamond entered China in the 1990s, China has rapidly developed into the world's second-largest natural diamond consumer. In 2009, China's imports of polished diamond jewelry exceeded Japan's, becoming the world's second-largest natural diamond retail market. Globally, China is the most important producer of lab-grown diamonds and the most promising lab-grown diamond consumer in the future. However, there are not many research results on the consumption of lab-grown diamond in China, which seriously restricts the development of China's lab-grown diamond retail market. In 2023, China's lab-grown diamond retail market developed rapidly, with lab-grown diamonds and jewelry being accepted by a wider range of consumer groups. Lab-grown diamond will became one of the most innovative products in China's jewelry market. To fully reflect the development status of China's lab-grown diamond market, this study is based on the current development status of China's lab-grown diamond retail market and rough diamond market, combined with relevant research results from the US lab-grown diamond retail market and China's natural diamond retail market, to explore the development path and future trends of China's lab-grown diamond.  Progress  The study finds that China's lab-grown diamond retail market now shows great development potential. Compared with the past market of hundreds of billions of natural diamonds, the future market size of lab-grown diamonds is very worthy of attention. At the same time, due to China's advantages in new media and online live broadcasting, it is expected that with the promotion of new media and the expansion of sales channels through online live broadcasting, the rapid development of China's lab-grown diamond retail market will be significantly promoted. Although the lab-grown diamond market has grown significantly, it also faces severe challenges.   Conclusions and Prospects  This paper suggests that the joint efforts and collaboration of all stakeholders are needed to build a sustainable development model for China's lab-grown diamond industry, so as to better promote its healthy development. Looking to the future, with the continuous deepening of theoretical research on the retail of China's lab-grown diamond market, and with the continuous improvement in the awareness level of Chinese lab-grown diamond consumers, in the context of the rapid development of the lab-grown diamond retail market to meet the needs of segmented consumer markets, China's lab-grown diamond industry will definitely have a very bright future. However, this also requires all stakeholders in China's lab-grown diamond industry to attach great importance to it, and work together to promote the healthy development of the industry. This study provides valuable insights for scholars, industry professionals and institutions interested in the development of China's lab-grown diamond retail market. In addition, this paper also provides practical guidance for the development of China's lab-grown diamond retail market.
Numerical simulation of multi-principal elements high-entropy alloy milling based on minimal quantity lubrication
WU Yanwei, LIU Yin, SUN Xingwei, YANG Heran, DONG Zhixu, ZHANG Weifeng
2025, 45(3): 332-341. doi: 10.13394/j.cnki.jgszz.2023.0265
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  Objectives  High-entropy alloys (HEA) with multi-principal elements have many excellent characteristics such as high strength, high hardness and high wear resistance, which have attracted widespread attention from scholars. However, the mechanical processing of HEA is difficult. This study utilizes minimal quantity lubrication (MQL) technology for milling HEA to improve their machining performance and explore the influences of different milling parameters on their milling force.   Methods  The thermodynamic coupling milling model of HEA (CoCrFeNiMn) and a four-edge end milling cutter is established using finite element simulation software. The difference in milling force between MQL milling and dry milling is studied by analyzing the material removal mechanism, and the influences of different milling parameters on milling forces are studied by single-factor experiments. Firstly, the three-dimensional model of the four-edge end milling cutter, the J-C constitutive model of HEA (CoCrFeNiMn), the heat conduction model and the contact friction model are established, and the material failure separation criteria are determined and the milling model is established. Then, the material removal mechanism under the thermodynamic coupling condition is analyzed, and the changes in milling forces between MQL milling and dry milling are analyzed from the perspectives of equivalent stress, contact friction and the thermal softening effect, and the advantages of MQL technology for milling HEA (CoCrFeNiMn) are analyzed. Finally, the effects of feed speed, spindle speed and milling depth on milling force are obtained by single-factor tests.  Results  Through comparative experiments between dry milling and MQL milling, it is found that: (1) The equivalent stress produced by the two milling methods are concentrated in the first deformation zone, and the equivalent stress of dry milling is also concentrated in the position near the cutting edge. (2) The equivalent stress value of MQL milling in the first deformation zone is slightly greater than that of dry milling. (3) The heat generated by the two milling methods is concentrated in the first deformation zone and the chips, and the chips take away most of the heat. The chip temperature generated by dry milling is significantly higher than that generated by MQL milling. (4) MQL milling significantly reduces the temperature at the cutting site and improves chip integrity. (5) When the milling depth is 0.15 to 0.20 mm, the milling force of MQL milling is basically the same as that of dry milling. When the milling depth is greater than 0.20 mm, the ability of MQL milling to reduce milling force increases with the increase of milling depth. This is due to the use of MQL technology in the milling process, which compensates for the reduced milling force caused by low friction coefficient and the increased milling force caused by weak thermal softening effect. The MQL milling single-factor tests show that: (1) The milling force increases with the increase of feed speed, and decreases with the increase of spindle speed, that is, it increases with the increase of feed rate per tooth. (2) The milling force increases with the increase of milling depths, and the effect of feed rate per tooth on the average milling force is gradually intensified with the increase of milling depth.   Conclusions  The MQL milling has obvious advantages, which can significantly reduce milling force at milling depth greater than 0.20 mm, and the ability to reduce milling force increases with the increase of milling depth. In addition, the use of MQL technology in the milling process can significantly reduce the temperature at the cutting position, improve HEA machining accuracy, and avoid a series of defects of traditional pouring lubrication. The cutting force in MQL milling conforms to the change law of cutting force in most metal milling with the process parameters. In MQL milling, the milling force can be further reduced by increasing the spindle speed and reducing the feed speed. When the milling depth is large, the spindle speed should be further increased and the feed speed should be reduced to reduce the feed per tooth, in order to deal with the high sensitivity of the milling force to the milling depth.
Temperature simulation analysis and wear experimental of diamond abrasive grains cutting steel mixed materials
WEI Min, SHI Yongjin, GUO Zihang
2025, 45(3): 342-351. doi: 10.13394/j.cnki.jgszz.2024.0128
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  Objectives  Diamond wire saw cutting, being environmentally friendly and unaffected by water depth, structure material, shape, or size, has become the preferred method for dismantling large oceanic structures. However, when cutting jackets above the water surface, the elevated temperatures in the cutting zone can lead to excessive wear on the wire saw and even result in cutting failure. To address this issue, this paper integrates theoretical, simulation, and experimental analyses to examine the impact of various cooling conditions on cutting zone temperature and tool wear. Furthermore, it identifies an optimal cooling method for the dismantling process of jackets using diamond wire saws on the sea surface.  Methods  First, based on the principles of thermal conductivity, a theoretical model of the temperature field in the cutting zone of diamond grains is developed to analyze the influence of cutting and media parameters on heat generation. Next, using AdvantEdge simulation software, a kinetic simulation model of diamond grit cutting reinforced concrete materials is established under various working conditions, including dry cutting, low-temperature air cooling, high-pressure water cooling, liquid nitrogen cooling, and low-temperature spray cooling. The temperature rise in the cutting zones under different cooling methods is analyzed. Finally, experimental cutting tests using diamond wire saws on reinforced concrete material workpieces are conducted to investigate the failure behavior and wear rate of the wire saws under different cooling conditions. The optimal cooling method is then identified and validates the simulation results.  Results  (1) According to the theoretical model of the temperature field in the cutting zone, the surface temperature increases with higher cutting parameters such as feed speed, cutting speed, and cutting time, while it decreases with the increase of medium parameters such as specific heat capacity and thermal conductivity. (2) The cutting simulation study indicates that under dry cutting conditions, the temperature in the cutting zone exceeds the diamond carbonization threshold, significantly compromising the cutting performance of the wire saw. In contrast, all four cooling methods maintain the cutting zone temperature below the diamond carbonization threshold, with low-temperature spray cooling demonstrating the most effective reduction in tool wear. (3) By measuring changes in the outer diameter of the beads on the wire saw, the lowest wear rate is observed under low-temperature spray cooling, which further validates the findings of the cutting simulation study. (4) Scanning electron microscope analysis of the worn diamond abrasive grains reveals four distinct behaviors of wear: intact abrasive grains, abrasive edge wear, surface fragmentation, and abrasive grain detachment. (5) Compared to dry cutting, low-temperature spray cooling increases the percentage of intact abrasive grains from 18% to 31% and reduces the abrasive grain detachment rate from 39% to 24%, thereby significantly enhancing cutting efficiency and extending the service life during diamond wire saw cutting of reinforced concrete materials.  Conclusions  When dismantling platform structures on the sea surface using diamond wire saws, low-temperature spray cooling is prioritized due to its minimal temperature rise in the cutting zone and the lowest bead wear rate. This approach significantly enhances cutting efficiency and extends the service life of the diamond wire saw.
Effect of tool angle in nanocutting of single crystal GaN using diamond cutter
WANG Yongqiang, XIA Hao, HU Zhihang, ZHANG Shuaiyang, YIN Shaohui
2025, 45(3): 352-365. doi: 10.13394/j.cnki.jgszz.2024.0186
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  Objectives  Single-crystal gallium nitride (GaN) is a pivotal semiconductor material widely utilized in high-power, high-frequency electronic devices, and optoelectronic applications. However, its inherent hardness and brittleness pose significant challenges in achieving damage-free surfaces during ultra-precision machining. Understanding the fundamental deformation mechanisms induced by cutting, particularly the critical role of tool geometry, is essential for advancing GaN machining technology. This study aims to comprehensively elucidate the influence mechanism of diamond tool angles, specifically the rake angle and flank angle, on the cutting-induced deformation behavior and subsurface damage formation in single-crystal GaN at the nanoscale. The primary objective is to establish clear relationships between tool angles, material removal mechanisms, defect generation (dislocations, phase transformation, amorphization), and final surface integrity, thereby providing foundational knowledge for optimizing ultra-precision machining processes.   Methods  To achieve these objectives, a rigorous multi-scale investigation is conducted, combining molecular dynamics simulation with experimental verification. Large-scale MD simulations are meticulously performed to model the nanoscale cutting process of single-crystal GaN using a diamond tool. The simulations employed highly validates interatomic potentials capable of capturing the complex bonding and deformation behavior of GaN. The model incorporates realistic crystal orientations and environmental conditions. The influence of tool angles is systematically explored by simulating cutting processes with a wide range of rake angles (−18°, −12°, −6°, 6°, 12°, 18°) and flank angles (−18°, −12°, −6°, 6°, 12°, 18°). Post-simulation analysis utilizes sophisticated algorithms to dissect the deformation mechanisms: employed to identify, characterize, and quantify the evolution of dislocations, including their types (e.g., perfect dislocations, partial dislocations), Burgers vectors, and densities within the workpiece. Used to distinguish between the pristine wurtzite GaN structure, transformed phases (e.g., possible local zinc-blende or other metastable structures under high stress), and amorphous regions generated during cutting. Local atomic stress (Von Mises or equivalent stress) and strain distributions are calculated and visualized to correlate mechanical loading with observed deformation and damage. Atomic kinetic energy is tracked to map the temperature evolution within the cutting zone and subsurface layers. To corroborate the simulation findings, controlled nanocutting experiments are conducted on single-crystal GaN substrates. Crucially, two distinct diamond abrasive grains with differing morphologies are employed as cutting tools: rake angle of −70° and a flank angle of 10°; rake angle of −43° and a flank angle of 20°.This direct comparison allows for the experimental assessment of the impact of varying rake and flank angles on surface morphology, chip formation behavior, and subsurface damage extent, using techniques such as transmission electron microscopy (TEM) and optical microscopy for cross-sectional analysis.  Results  The integrated simulation and experimental approach yields profound insights into the role of tool angles: Increasing the positive rake angle or reducing the magnitude of a negative rake angle is found to significantly enhance the shear-dominated material removal mechanism. This promotes more efficient and continuous chip formation while effectively suppressing undesirable lateral atomic flow and material pile-up at the groove sides, leading to improved groove definition. Conversely, increasing the magnitude of the negative rake angle dramatically exacerbates subsurface damage. The highly compressed wedge beneath the tool tip induces severe plastic deformation deeper into the substrate. Comprehensive analysis using DXA, and stress-strain fields reveals the fundamental mechanisms triggered by large negative rake and flank angles: These tool geometries induce substantially higher compressive and shear stresses within the primary deformation zone directly ahead of the tool and the subsurface region. Consequently, localized temperatures rise significantly due to intense plastic work and friction. The extreme mechanical and thermal loading promotes prolific nucleation of dislocations. These dislocations readily propagate and interact, forming complex networks. The high von Mises stress and shear stress beneath the tool facilitate solid-state phase transformations from the stable wurtzite structure to other phases. Furthermore, the intense deformation and temperature lead to extensive amorphization (loss of long-range crystalline order) within the subsurface layer. Employing tools with positive rake angles and adequate positive flank angles demonstrably alleviates subsurface damage. The cutting mechanics shift towards efficient shearing at the primary shear zone, minimizing the crushing effect below the tool. This promotes cleaner material removal, reduces dislocation density and amorphization depth, and consequently facilitates the generation of high-quality surfaces with minimal subsurface damage. Nanocutting experiments using the two specific diamond grains provids clear validation. more negative rake consistently produced scratches with significantly greater pile-up, more pronounced lateral cracks, and deeper subsurface damage zones compared to less negative rake and larger flank angle, as evidenced by TEM characterization. This directly supports the simulation predictions regarding the detrimental effects of highly negative rake angles.   Conclusions  This comprehensive study, synergizing high-fidelity molecular dynamics simulations with targeted experimental validation using distinct tool geometries, has significantly deepened the understanding of the nanoscale deformation and damage mechanisms in single-crystal GaN during diamond cutting. It unequivocally establishes that: Tool rake angle is a paramount factor governing the dominant material removal mode, chip formation efficiency, and the severity of subsurface damage. Large negative rake angles, while sometimes necessary for tool edge strength, induce extreme stress and temperature conditions that promote massive dislocation activity, phase transformation, and amorphization, leading to deep subsurface damage. Positive rake angles and sufficient positive flank angles promote shear-dominated cutting, suppress deleterious lateral flow and deep damage, and are highly conducive to achieving superior surface integrity with minimal subsurface defects. The mechanistic insights gained, particularly the detailed characterization of defect evolution (dislocations, phase changes, amorphous layers) linked directly to specific tool angles, provide crucial theoretical guidance and a robust scientific foundation for the rational design and optimization of ultra-precision machining (e.g., diamond turning, grinding, polishing) processes for single-crystal GaN. This knowledge is vital for enhancing the performance and reliability of next-generation GaN-based devices.
Experiment and simulation of single diamond abrasive particle scratching RB-SiC composite material
ZHANG Dehan, DING Kang, CAI Xintong, YANG Feng, DONG Zhigang, BAO Yan, GUO Xiaoguang, KANG Renke
2025, 45(3): 366-376. doi: 10.13394/j.cnki.jgszz.2024.0053
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  Objectives  Reaction-sintered silicon carbide (RB-SiC) composite materials have excellent properties such as high specific stiffness, high hardness, and corrosion resistance, and are widely used in important equipment such as space telescopes and aerospace combustion chambers. However, the high hardness and brittleness lead to many defects when processed using traditional methods. To investigate the material removal mechanism and the surface damage causes during the grinding process of RB-SiC composite materials, the ABAQUS finite element software is used for scratch simulation and the scratching experiment of a single diamond abrasive indenter is used for verification.  Methods  Based on ABAQUS finite element simulation software, a scratch simulation model of RB-SiC composite material with a multiphase structure is constructed. The model uses a continuously distributed Si and β - SiC mixture as the matrix, characterized using the Drucker Prager elastoplastic constitutive model. The SiC reinforcement phase distributed in particle or powder form is characterized using brittle fracture as the failure criterion, and a zero-thickness cohesive unit interface layer is established between the two phases. The relationship between the scratch force and the scratch depth is investigated by a single abrasive particle scratch experiment, and compared with the simulation model. The material removal mechanism and the causes of surface damage are then obtained.  Results  In the simulation, it is found that the variation of scratching force is closely related to the relative position between the particles and the pressure head. The scratching forces of particles in the middle of the trajectory suddenly increase, while particles above the trajectory have a smaller impact on scratching force. The particles below the trajectory have a slightly smaller impact on scratching force than those above. When the pressure head penetrates the middle of the particle, its stress is greater than the particle fracture strength, causing transgranular fracture of the particle. At the same time, the crack continues to propagate to the boundary between the two phases and deflects along the boundary. The particles above the trajectory will be removed as a whole with the removal of the matrix material. When multiple particles are in close proximity and sequentially in contact with the indenter, the stress concentration during the fragmentation of the front particles and the plastic deformation of the matrix is greater than the fracture stress of the rear particles, resulting in the collapse of the rear particles before they come into direct contact with the indenter. The deformed matrix that has lost particle support and has not been completely removed will be pushed to the next particle by the indenter, causing a sudden drop in scratching force. The scratch experiment shows that the crushing width of the scratch path increases with the increase of scratch depth. When the scratch depth is 5 μm, the material surface is relatively flat, and the material is mainly removed by plastic deformation of the matrix. When the scratch depth increases to 30 μm, the brittle peeling phenomenon of the material becomes more and more obvious, and the surface morphology of the material also deteriorates. It can be observed that the cleavage and fragmentation of particles, the voids formed by particle extraction, the transverse cracks, and the matrix delamination and fan-shaped fracture zone are caused by the diagonal downward propagation of the medium diameter crack. This is because the scratch depth is much greater than the plastic brittle transition depth of the material, and the material is mainly removed by brittleness.  Conclusions  By establishing a two-phase finite element simulation two-dimensional model for single abrasive particle scratching simulation and conducting experimental verification, it is found that the surface morphology of scratches deteriorates with increasing scratching depth, and the scratching force gradually decreases with decreasing scratching depth. Moreover, the simulation and the experimental scratching force values for small scratching depths are in good agreement. The relative position between the SiC particles and the diamond indenter tip trajectory, as well as the spacing between the SiC particles, leads to changes in scratching force. The SiC particles located above the trajectory will cause the scratching force to increase significantly. When the scratch depth is shallow and there are no original SiC particles near the surface, plastic removal will still occur. The subsurface cracks start at the particle-matrix interface and spread along the particle phase boundary to form micro-cracks. When the outlet support of the material is insufficient, the micro-cracks of different depths will expand and converge, eventually producing the phenomenon of material edge collapse. This study provides a theoretical basis and simulation verification for the removal mechanism and damage formation causes of RB-SiC materials.
Magnetic particle grinding and finishing test of mixed particle size abrasives
LIU Bingyang, DING Yunlong, SHAO Wenjie, HAN Bing, CHEN Yan
2025, 45(3): 377-384. doi: 10.13394/j.cnki.jgszz.2024.0078
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  Objectives  Magnetic particle grinding finishing technology as an advanced processing technology can achieve high precision surface treatment. In order to simplify the test device, reduce the test cost and improve the processing effect, the single particle size abrasive is changed to mixed particle size abrasive without changing the test device, so as to improve the grinding effect of magnetic particles.  Methods  Finite element analysis software is used to simulate the magnetic field in the machining area, and the magnetic field data is imported into the discrete element simulation software through an API interface to obtain the magnetic field during the simulation process, in order to simulate the force situation of mixed particle size abrasive and single particle size abrasive during machining. Taking the spindle speed of the machine tool (A), the abrasive mass ratio (B) and the abrasive particle size ratio (C) as the research objects, the experimental parameters are analyzed and optimized using response surface methodology. To prevent abrasive splashing and reduce the grinding effect, the selected experimental parameters ranges are 400 to 600 r/min for A, 0.50 to 2.00 for B, and 1.5 to 2.5 for C. Using the surface roughness Ra of the workpiece as the response value, the Box Behnken method is used for response surface test design.  Results  The P-value of the variance analysis of the model experiment results is less than 0.000 1, indicating that the experimental model is highly significant. The mismatch term refers to the unexplained error in the model, with a P-value of 0.458 1, much greater than 0.050 0, indicating that the mismatch term is not significant and the regression equation fitted by the software is valid. At the same time, the multiple correlation coefficient R2 is 0.996 2, and R2Adj is 0.989 4 after verification, which is very close to 1.000 0, indicating a good fit of the model. Moreover, the surface roughness is affected by the spindle speed, abrasive mass ratio and abrasive particle size ratio to 98.94%. The results of the single factor experiment indicate that the order of influence on surface roughness Ra is the spindle speed, followed by the abrasive mass ratio and the abrasive particle size ratio. When the spindle speed is 500 r/min and the abrasive mass ratio is 1.25, the workpiece surface roughness Ra reaches the minimum value. In the case of a certain abrasive mass ratio, when the abrasive particle size ratio is 2.0 and the spindle speed is 500 r/min, the workpiece surface roughness Ra reaches its minimum value. Under the condition of constant spindle speed, when the abrasive mass ratio is 0.50 and the abrasive particle size ratio is 2.5, the workpiece surface roughness Ra reaches the maximum. However, when the abrasive particle size ratio is 2.0 and the appropriate mass ratio is 1.25, the surface roughness Ra of the workpiece can reach the minimum value. Aiming at the minimum surface roughness Ra of the workpiece, the response surface software is used to optimize the data, and the optimal process parameter combination for workpiece processing is obtained, that is, the spindle speed is 511 r/min, the abrasive mass ratio is 1.67, the abrasive particle size ratio is 1.9, and the predicted surface roughness Ra value after processing is 0.038 µm. When the workpiece is machined under the optimal process parameters, the surface roughness Ra of the workpiece decreases from the original value of 0.244 μm to the test value of 0.036 μm, and the absolute value of relative error between the two is 5.26%.  Conclusions  The experimental results show that the established model is effective, and the process parameters that affect the surface roughness Ra of the workpiece are in the order of spindle speed, followed by abrasive mass ratio and abrasive particle size ratio. Compared to single-abrasive magnetic particle grinding, the use of mixed abrasives can further reduce the surface roughness of the workpiece and improve its machining effect.
Modeling and finite element simulation of temperature field in rail abrasive belt grinding
WANG Haipeng, LI Jianyong, ZHAO Chaoyue, LIU Yueming
2025, 45(3): 385-395. doi: 10.13394/j.cnki.jgszz.2024.0050
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Abstract:
  Objectives  Rail is an important component of rail transit, carrying train loads and guiding vehicle direction in service. Due to worn-outs and shocks during service, rails can cause various defects such as corrugation, spalling and squat, which seriously threaten the safety of train running, reduce the stability of train running and produce huge running noise. The use of sand belt grinding to remove the surface material of steel rails can remove surface defects and achieve the goal of extending the service life of steel rails. However, during the grinding process, a large amount of grinding heat will be generated in the grinding area between the sand belt and the rail, causing the temperature of the rail to rise. Due to differences in temperature distribution and cooling rates, residual stress will be generated on the surface of the rail, and martensitic burns may occur in severe cases, reducing the service life of the rail and accelerating the rate of rail damage. Therefore, it is necessary to accurately control the grinding temperature during rail grinding, and accurately grasp the influence law of rail grinding parameters on the grinding temperature, so as to further improve the grinding quality of rails and extend their service life.  Methods  Based on elastic contact theory and the grinding process of an abrasive belt rail driven by a concave contact wheel, a contact pressure distribution region model of the rail surface is established. According to the principles of grinding heat generation and conduction, a grinding surface temperature distribution model of the abrasive belt rail is established, and the accuracy of the model is verified by simulation analysis. At the same time, the variation rule of grinding temperature under the influence of grinding power, grinding speed and sand belt speed is analyzed, and the distribution of grinding temperature in the rail subsurface is studied.  Results  Firstly, based on the theory of elastic contact and the abrasive belt rail grinding process driven by a concave contact wheel, the actual contact situation between the rail and the abrasive belt is further simplified to make the contact problem more universal and regular. The contact model of rail abrasive belt grinding is solved based on Hertz contact theory, and the distribution shape of the contact area is obtained. And based on the contact model, the maximum stress model of the area is solved, and the relationship between the concentrated grinding positive pressure during the grinding process and the distribution of grinding pressure in the contact area is established, obtaining the grinding pressure distribution model. Secondly, based on the grinding pressure distribution model, the total energy of the grinding area is obtained, and the form of conversion from grinding energy to grinding heat is analyzed. The thermal flow rate in the grinding area is analyzed and integrated, and the discrete point heat source set generated by multi-abrasive grinding is transformed into a continuous surface heat source. The total heat in the grinding zone is calculated based on the grinding power and grinding contact area. The relevant theory of ultimate chip energy is applied to solve the heat flow into the chip. Based on the energy distribution model of a single abrasive grain rubbing on the workpiece surface and the heat distribution ratio between the rail and the belt, the heat flow into the rail is calculated. Based on the transient point heat transfer model in heat conduction theory, the multiple discrete moving point heat source set is transformed into a moving surface heat source model according to the generation and conduction mechanism of grinding heat. The dynamic temperature distribution model and the maximum temperature solution model for the rail grinding surface are constructed. Finally, the simulation model of the temperature field in the grinding area is established based on the heat transfer model of the rail abrasive belt, the grinding pressure distribution model, and the general thermal conductivity differential equation derived from the variational principle of heat transfer and the Gaussian formula. The mathematical model is validated using simulation analysis. At the same time, the influence mechanism of the grinding power, grinding speed, and abrasive belt speed on grinding temperature and the variation law of grinding temperature are analyzed, and the grinding temperature distribution of the rail subsurface is studied.  Conclusions  The highest temperature in the grinding zone is positively correlated with the grinding power and the abrasive belt speed, and negatively correlated with the grinding speed. Moreover, the influence of grinding speed on temperature is the most significant. Therefore, in the process of rail abrasive belt grinding, a higher grinding speed should be used as much as possible to reduce the grinding temperature. At the same time, the increase in abrasive belt speed has a significant effect on temperature rise, so the grinding power should be increased first and then the abrasive belt speed should be increased when the grinding efficiency is increased.
Temperature simulation and experimental for polishing TC4 with abrasive cloth wheel
WANG Libo, XIAN Chao, XIN Hongmin
2025, 45(3): 396-407. doi: 10.13394/j.cnki.jgszz.2024.0019
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Abstract:
  Objectives  During the polishing and grinding process, a large amount of heat is generated in the contact area between the grinding tool and the workpiece, while the amount of material removed is very small. Most of the heat is transferred to the workpiece, causing a rapid increase in temperature near the surface of the workpiece. This results in adverse effects such as residual tensile stress, white layer, and deformation, which negatively impact the surface quality and performance of parts. Therefore, studying the distribution laws and influencing factors of surface temperature in polishing and grinding, and controlling the processing surface temperature are of great significance.  Methods  A polishing test platform is built, and polishing temperatures are measured under different process parameters. The measured temperature values are corrected to obtain the actual temperature values. A theoretical model of the temperature field in the polishing contact area is derived based on the rectangular moving heat source model, and a temperature calculation model corresponding to the experimental measurement point is obtained, with the temperature value of that point calculated. The workpiece temperature field distribution during polishing is obtained using ANSYS simulation software and APDL for cyclic loading. The distribution law of the workpiece temperature field is studied, and the internal mechanism of this distribution law is explored. The temperature values corresponding to the experimental measurement points are extracted. The measured, calculated, and simulated values of temperature near the same point in the polishing contact area are compared. Based on the experimental results, single factor influence law figures of four process parameters on polishing temperature are drawn, and the influence mechanisms of the four process parameters on polishing temperature are explored. Based on the relationship between the radius increment and compression depth of abrasive cloth wheel, flexible polishing and rigid polishing are defined, and the effects of flexible and rigid polishing on polishing temperature are explored. A main effect analysis of process parameters is conducted with polishing temperature as the response and process parameters as the factors, to study the degree of influence of each process parameter on polishing temperature.   Results  Comparing the measurement results, calculation results, and simulation results of polishing temperature, it is found that the deviation rates between the simulation values and the measurement values are less than 22%, and the devia-tion rates between the calculated values and the measurement values are less than 17%. The deviations between simu-lated values and measured values are mainly due to the actual heat source model being complex, while the simulated heat source model uses a simplified rectangular heat source model, as well as measurement errors. The deviations between calculated and measured values are mainly caused by measurement errors in contact arc length, temperature, heat distribution coefficient, and the heat source model. The influence of four process parameters on polishing temperature is as follows: polishing temperature increases with the increase of spindle speed, because higher spindle speed results in greater linear velocity of the abrasive cloth wheel, and more work is done by the frictional force between the abrasive particles, binder, and workpiece per unit time, generating more heat and resulting in higher polishing temperature; polishing temperature increases with the increase of the compression depth of the abrasive cloth wheel. This is because larger compression depth leads to greater tangential force on a single abrasive particle, and more abrasive particles participate in cutting. More work is done by the frictional force between the abrasive particles, binder, and workpiece per unit time, generating more heat, and resulting in higher polishing temperature; polishing temperature decreases with the increase of feed rate. Although higher feed rate enhances heat source intensity, the contact time between the workpiece and the heat source is shorter, resulting in less heat transferred to the workpiece and lower polishing temperature; polishing temperature decreases with the increase of mesh number of abrasive particles. This is because a larger mesh number of abrasive particle means smaller abrasive particle size and more abrasive particles interacting with the workpiece in the contact area, making heat more easily carried away by the abrasive particles. At the same time, the larger the mesh number of abrasive particle, the smaller the abrasive particle size, the larger the contact area between the workpiece and grinding tool, the smaller the tangential force exerted on a single abrasive particle, and the less work done by frictional force between the abrasive particle and the workpiece per unit time, generating less heat. These two reasons together lead to a decrease in polishing temperature with the increase of mesh number of abrasive particles. A main effect analysis shows that compression depth has the largest main effect and the greatest influence on polishing temperature, while the other three process parameters have smaller main effects and less influence on polishing temperature.   Conclusions  The value of compression depth has the greatest influence on the polishing temperature and also affects whether the polishing state is rigid or flexible. Therefore, when determining the polishing process parameters, the appropriate compression depth should be selected first, and then other process parameters should be selected accordingly.
Modelling of circumferential surface topography of grinding wheel with random distribution of circular truncated cone abrasive grains
CHEN Xiaodong, WANG Dexiang, GUO Feng, LI Xinming, JIANG Jingliang
2025, 45(3): 408-415. doi: 10.13394/j.cnki.jgszz.2024.0086
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Abstract:
  Objectives  Due to the complexity of the grinding process, the study of the grinding mechanism has always been a research hotspot in the field of precision grinding. The establishment of an accurate surface topography model of the grinding wheel circumference is an important basis for studying the grinding mechanism. The surface topography of the corundum grinding wheel is accurately described using four parameters, namely the shape of the abrasive grain, the size of the abrasive grain, the height of the abrasive grain bulge and the number of abrasive grains per unit area. The corresponding grinding wheel model is established using Matlab.  Methods  To construct a circumferential surface morphology model of the corundum grinding wheel using Matlab simulation software, the geometric shape of the abrasive particles is first simplified to a truncated cone with a cone angle of 45° based on the actual shape of the abrasive particles in the corundum grinding wheel. By using the center coordinates of the large and small circular surfaces of the truncated cone abrasive particles and the radius variation relationship at different axial heights, an arbitrary truncated cone particle with size d is constructed using the cylinder function. Secondly, based on the corresponding grinding wheel circumferential surface established in the cylindrical coordinate system, the rand random function is used to randomly generate Nt grinding particle position coordinates on the circumferential surface. Based on the phenomenon that the grinding particle size and the protrusion height both follow the normal distribution law, the normrnd function is used to generate circular truncated grinding particles with randomly distributed positions on the grinding wheel circumferential surface. Then, a collision detection method is used to check whether there is interference between the abrasive grains, that is, the distance between the centers of the small circular surfaces of any two adjacent truncated cone abrasive grains should be greater than or equal to the sum of the radii of the large circular surfaces of the two abrasive grains. Finally, the real grinding wheel surface topography and the constructed grinding wheel surface topography model are compared and analyzed to determine the accuracy of the modeling method in this paper.  Results  A corundum grinding wheel model is constructed with a diameter and width of 20 mm and 4.5 mm, particle size code of F80, grinding wheel structure number of 7, abrasive rate of 48% and grinding particle size of 152 to 178 μm. The following results are obtained: (1) The distance between any adjacent truncated cone abrasive grains is narrow, and there is no interference between abrasive particles. The position distribution of abrasive particles on the surface of the grinding wheel is in accordance with the random distribution characteristics, and the surface topography of the grinding wheel produces blocky and narrow strip-shaped gap areas. (2) The total number of abrasive grains calculated theoretically is 9 342, while the total number of abrasive grains generated in the model is 8 626, with a relative error between the two of only 7.66%. (3) The size distribution of the abrasive grains and the protrusion height distribution of the abrasive grains in the model are statistically analyzed, and it is found that the distribution patterns are consistent with the normal distribution curve set in the modeling.  Conclusions  The abrasive grain shape can be set to a truncated cone with a cone angle of 45°, and the size of the truncated cone abrasive grains can be converted from spherical abrasive grains based on the principle of volume invariance, which aligns with the actual abrasive grain shapes observed in real grinding wheels during the grinding process. Compared with the traditional modeling method for grinding wheel morphology, the modeling method proposed in this paper does not require complex coordinate transformations between the grinding wheel circumferential surface and its unfolded plane, and can obtain a model of the grinding wheel circumferential surface morphology where the size of the truncated cone abrasive grains and the height of the protrusions follow the normal distribution law, and the position of the abrasive particles are randomly distributed. The model has high similarity to the distribution characteristics of real grinding wheel topography, and the grinding wheel surface forms irregular block-shaped and narrow strip-shaped gap areas. Therefore, this modeling method is suitable for the establishment of a corundum grinding wheel circumferential surface topography model. The microscopic contact mechanism between the grinding wheel and the workpiece surface can be further explored through this model, and a grinding surface topography prediction and analysis model can be established.
Surface morphology segmentation and evaluation of diamond lapping pad based on improved Mask R-CNN
SUO Wenlong, LIN Yanfen, FANG Congfu
2025, 45(3): 416-426. doi: 10.13394/j.cnki.jgszz.2024.0080
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Abstract:
  Objectives  The surface morphology of diamond lapping pads has a direct impact on the lapping quality of hard and brittle materials such as sapphire and silicon carbide. Detecting and controlling the surface morphology of diamond lapping pads is a crucial step in improving the lapping quality. Collecting surface images of diamond lapping pads, which contain numerous tiny abrasive particles, pores, and complex background textures, makes it challenging to conduct quantitative detection of their surface morphology. An improved Mask R-CNN model and three parameter evaluation indicators, namely the target number recognition accuracy, target segmentation area accuracy, and target position error, are utilized to explore the segmentation performance and effect of the proposed model.   Methods  Based on the Mask R-CNN model, the dilated convolution method is adopted to improve the feature extraction network in the model's backbone. The ResNet50, which serves as the feature extraction network in the backbone, is divided into five stages: Input stem and stages 1 to 4. The network structures of the Input stem, stages 1, 2, and 4 are kept unchanged. Dilated convolution is introduced in stage 3, and each residual block in stage 3 is improved into a residual block using dilated convolution to expand the receptive field, enhance the model's ability to extract deep semantic features of abrasive particles and pore targets of smaller scales on the surface of the lapping pad, and improve segmentation performance for abrasive grain and pore targets of different scales. The loss function and mean average precision (mAP) of Mask R-CNN are used to comprehensively reflect the performance of the model. For evaluation of the segmentation effect, three parameters, namely target number recognition accuracy, target segmentation area accuracy, and target position error, are proposed. These are mainly calculated based on the number, area, and center of abrasive particles and pores, and evaluating diamond abrasive particles and pores separately to assess the overall surface morphology of the lapping pad.  Results  Through training and verification of the improved Mask R-CNN model, results show that this method can realize the recognition and segmentation of diamond abrasive particles and pores in the surface images of the lapping pad, achieving an mAP of 78.2%. By comparing the surface images of the lapping pad with the model segmentation images, there is no significant difference between the number of diamond abrasive particles and pores obtained by the improved Mask R-CNN model and the actual numbers, indicating that this method effectively recognizes and segments diamond abrasive particles and pores. Comparing the model's segmentation results with manually annotated results and calculating the three evaluation indicators, the recognition accuracies for the number of diamond abrasive particles and pores are 82.1% and 93.4%, respectively. This is due to the complex background of the lapping pad's surface images and unclear contrast between abrasive particles, pores, and binders, which can cause some missed or false detections when using this method. For successfully identified diamond abrasive grain and pore targets, the segmentation area accuracies are 89.9% and 95.3%, respectively, indicating small differences between segmented abrasive areas and actual areas, with a high degree of agreement, and good classification and segmentation performance by the model. By comparing the contours of diamond abrasive particles and pores obtained by model segmentation with the actual contours, the position errors are 3.80% and 2.80%, respectively, indicating small differences between the segmented and actual contours, and demonstrating good segmentation accuracy.   Conclusions  The dilated convolution method can effectively expand the receptive field and improve the ability to extract deep semantic features of targets at different scales. Therefore, based on the comparison between the segmentation images of the improved Mask R-CNN model and manually annotated images and the evaluation of the three indicators, the improved Mask R-CNN model demonstrates good segmentation performance for diamond abrasive particles and pores of different scales on the lapping pad surface, proving the effectiveness of the segmentation method.