Abstract: Significance: The fabrication of high-performance optoelectronic devices requires substrate materials with exceptional optoelectronic properties, robust mechanical stability, and broad application versatility. These substrates are crucial for advancing the information technology sector and driving economic growth. Lithium niobate (LiNbO3) crystal has the advantages in piezoelectric, electro-optic, nonlinear optical, and photorefractive effects, and exhibits superior thermal stability, chemical resilience, and tenability, making it an ideal substrate for the development of optoelectronic components such as optical modulators, frequency doublers, and optical filters. The LiNbO3 crystal is quite promising for application in cutting-edge technologies, such as 5G communication systems, micro/nano-integrated photonics, and artificial intelligence. Achieving an ultra-smooth, low/no-damage crystal surface is paramount for LiNbO3-based optoelectronic devices. Any imperfections, such as scratches, cracks, or embedded abrasives, can lead to scattering, absorption, or diffraction of optical signals, adversely affecting device performance. However, the challenges posed by LiNbO3’s intrinsic properties—namely, its relatively low hardness, high brittleness, and significant anisotropy—complicate the precise surface processing. High-efficiency, high-quality, and low/no-damage ultra-precision machining technology for large-sized high-quality crystals is a critical bottleneck in enabling the widespread application of LiNbO3 crystal devices. Progress: Thinning, lapping, and polishing are essential for LiNbO3 crystals to meet industrial application requirements for high-performance optoelectronic devices. The stability and reliability of optoelectronic devices are significantly influenced by the generation and evolution of surface and subsurface damages. The hardness, fracture toughness, Young's modulus, and other material properties of LiNbO3 along different crystallographic orientations are investigated using methods such as nanoindentation and scratch tests. The surface damage patterns of various planes are analyzed. The material removal behaviors under different parameters are revealed. Ion slicing and grinding are two critical processes for thinning LiNbO3 crystals. Ion slicing, which relies on ion implantation and wafer bonding, enables the precise thinning of crystals. Currently, it is possible to produce high-quality LiNbO3 films with thicknesses varying from several hundred nanometers to a few micrometers. Grinding utilizes the mechanical behavior of abrasives to rapidly remove material from the LiNbO3 crystal. A crystal substrate with a thickness of 80 μm is prepared effectively by optimizing the grinding parameters. Free-abrasive lapping has a wide range of applicability. However, lapping for LiNbO3can easily lead to surface damage and abrasive embedding. During fixed abrasive lapping, abrasive embedding is effectively prevented, and surface and subsurface damage are reduced. It also exhibits notable advantages for continuous batch grinding. Chemical mechanical polishing is a widely adopted final polishing method that effectively reduces damage from previous processes, achieving a surface roughness (Ra) of less than 1 nm. With advancements in grinding and chemical mechanical polishing, techniques such as photolithography, etching, and femtosecond laser ablation have been employed to fabricate LiNbO3 crystal metasurfaces, facilitating the development and application of multifunctional and ultra-compact integrated optoelectronic devices. Additionally, innovative methods, such as optimizing polishing slurry compositions with nanomaterial additives and adaptive shearing-gradient thickening polishing, have enabled ultra-precision processing, achieving ultra-smooth and low/no-damage results. High-shear and low-pressure grinding and magnetorheological shear thickening polishing under the coupling of magnetic, stress, and flow fields hold significant promise for the ultra-precision polishing of LiNbO3 crystals. Conclusions and Prospects: As critical functional materials in advanced applications, such as 5G wireless communication, integrated/micro-nanophotonics, and big-data processing, LiNbO3 crystals have garnered significant attention for their potential in ultra-precision machining technologies. Research shows that the development and evolution of surface/subsurface damage have been examined using methods such as nano-indentation and scratch testing. Ion slicing and grinding are effective techniques for thinning lithium niobate crystals. Lapping and chemical mechanical polishing are commonly used techniques to achieve ultra-precision machining. Furthermore, high-quality LiNbO3 metasurfaces can be generated using micro-nano manufacturing methods such as femtosecond laser ablation, etching, and photolithography. New technologies, such as high-shear and low-pressure grinding and magnetorheological shear thickening polishing, are the most promising methods for achieving ultra-precision machining of LiNbO3 crystals. Considering the complex interplay between material properties, processing parameters, and underlying mechanisms, the ongoing exploration of new ultra-precision machining techniques and process optimizations for LiNbO3 crystals is critical. Such advancements are essential for enhancing machining efficiency, improving surface quality, and minimizing damage. However, future work, including the material removal mechanism of LiNbO3 crystals, the critical machining conditions of elastic-plastic-brittle transition, and surface/subsurface quality control, needs to be systematically studied to provide theoretical and technical guidance for the ultra-precision machining of LiNbO3 crystals. Given the fundamental challenges and technological implications, the ultra-precision machining of LiNbO3 crystals is expected to remain a focal point of research for the foreseeable future, warranting continued investigation and development in this field.
Abstract: Objectives: In superhard materials, polycrystalline diamond (PCD) has become a hot topic in scientific research because it inherits the advantages such as high hardness, high wear resistance, and high thermal conductivity from diamond. The type and content of the binder have a great influence on the properties of polycrystalline diamond. Methods: The microstructure of polycrystalline diamond samples is analyzed by FEI INSPECT F50 scanning electron microscope (SEM) of FEI Company in the United States, and the bonding state between diamond and binder is observed. The distribution of each element in the polycrystalline diamond sintered body is tested and analyzed by an energy dispersive spectrometer attached to the scanning electron microscope. An A8 ADVANCE X-ray diffractometer (XRD, λ = 0.154 06 nm, Germany, scanning speed: 10°/ min, scanning range: 20°～90°) is used to analyze the phase of polycrystalline diamond samples and raw materials to determine their phase composition. The sample density is measured by Archimedes' principle. The Vickers hardness of the sample is measured using a FM-ARS900 microhardness tester (load: 9.81 N, holding time: 10s). The fracture toughness is calculated using the fracture toughness formula according to the crack length, the hardness, and the elastic modulus of the material. Results: It can be concluded from XRD analysis that PCD is mainly composed of diamond, TiC, and Al4C3, and that the Ti3AlC2 phase is not detected in any sample. Therefore, Ti3AlC2 is considered to have been completely decomposed. The Ti-C bond in Ti3AlC2 is a strong covalent bond, while the Ti-Al bond is a weak metallic bond. In addition, Ti3AlC2 is a metastable phase, while TiC is stable at high pressure and high temperature. Therefore, Ti3AlC2 is decomposed into TiC and Al-Ti alloy, and Al-Ti reacts with diamond to form TiC and Al4C3. The existence of TiC and Al4C3 diffraction peaks also confirms this finding. From the SEM analysis, it can be concluded that when the binder content is 10% and 15%, there are a small number of holes and cracks on the surface of PCD; when the binder content is 20%, the diamond is tightly wrapped by the binder, and there are no obvious holes between the particles. The crystal form is complete without any fragmentation, and the diamond is arranged closely and distributed evenly, with better combination and compactness, indicating that the synthesis process of the PCD sintered body is well controlled. When the binder content is 25% and 30%, the excess binder appears to aggregate and cause dispersed diamonds and more holes. Moreover, no Ti3AlC2 grains with a layered structure were found under these conditions, which was consistent with the results of XRD analysis. Under high temperature and high pressure, the increase in Ti3AlC2 content will decompose more Al-Ti alloy into the liquid phase, which enhances the flow and uniform distribution of diamond and the generated hard phases in the system. At the same time, the product of Ti3AlC2 decomposition reacts with diamond under high temperature and high pressure to form TiC and Al4C3 with strong covalent bonds, which improves the bonding state between diamond particles, thus improving the comprehensive mechanical properties of PCD. The relative density shows a trend of increasing first and then decreasing. When the amount of binder is too much, the bonding performance between diamond and binder becomes worse, and the wear ratio decreases. In the electron microscope image, it is observed that the aggregation and porosity of the binder appear in the PCD composites, which explains the deterioration of mechanical properties. With the increase of Ti3AlC2 content, the Vickers hardness and fracture toughness of PCD increase first and then decrease. When the mass fraction of Ti3AlC2 is 20%, the hardness of PCD reaches the maximum value of 54.0 GPa. The fracture toughness of PCD reaches the maximum value of 5.23 MPa·m1/2 when the mass fraction of Ti3AlC2 is 25%. When the mass fraction of Ti3AlC2 is more than 20%, the high content of binder in the sintered body will lead to a decrease in the relative density of PCD, resulting in a decrease in the Vickers hardness of the sample. Conclusions: Polycrystalline diamond is prepared at 5.5 GPa, 1500 °C, and 6 minutes by using diamond with a particle size of 5 μm as raw material and Ti3AlC2 as the binder. The effect of Ti3AlC2 content on the structure and properties of PCD is studied. Ti3AlC2 completely decomposes and reacts with diamond under high temperature and high pressure. Diamond, TiC, and Al4C3 are the main components in the sintered body. The binder reacts with diamond to form TiC and Al4C3. Through the combination of TiC and Al4C3 as intermediates, the diamond particles are firmly bonded together to form a dense microstructure. An appropriate amount of binder makes the diamond and the bonding material evenly distributed, and the PCD sintered body becomes denser. When the mass fraction of Ti3AlC2 is 20%, the relative density, Vickers hardness, and wear ratio of PCD reach maximum values of 99.3%, 54.0 GPa and 5 733.3, respectively. When the mass fraction of Ti3AlC2 is 25%, the fracture toughness of PCD reaches the maximum value of 5.23 MPa·m1/2. When the Ti3AlC2 content reaches 25% and 30%, the density, hardness, and wear ratio of the PCD samples decrease due to the excessive aggregation and pores of the binder and diamond in the sintered body.
Abstract: Objectives: The diamond synthetic equipment in China is mainly the hinged cubic press (referred to as cubic press). With the acceleration of large-scale presses, the performance of cubic presses has greatly improved, but higher requirements have also been put forward for the assembly accuracy of these presses. In order to improve the centering accuracy of the top hammer of the cubic press, the assembly errors of the working cavity of the hinge beam for the cubic press are researched. Methods: Firstly, based on the small displacement torsor (SDT) theory, the assembly tolerance model of the hinge beam of the cubic press with different tolerance principles is established. Secondly, the space vector is used to represent the three-dimensional dimension chain. Based on the space vector ring superposition principle, the closed ring size and its variation calculation model representing the motion posture of the hinge beam piston top hammer is derived, and the possible error range of the intersection points between the bottom, the left, and the upper top hammer axes and their respective top hammer outer end faces are obtained. Finally, the cumulative closed-loop error FR obtained from the three-dimensional tolerance analysis of the single hinge beam piston top hammer posture is compared with the similar error X1 obtained from the one-dimensional dimensional chain analysis. At the same time, the Plackett-Burman design (PBD) is used to screen out the variables that have a significant effect on the sealing ring of the top hammer posture of a single hinge beam piston. Results: (1) Through the calculation of the three-dimensional tolerance analysis method established by the cubic press, it is found that the possible errors of the axis of the top hammer of the left hinge beam are [−0.070, 0.095] in the X direction, [−0.655, 0.655] in the Y direction, and [−0.855, 1.035] in the Z direction. The possible errors of the axis of the top hammer of the bottom hinge beam are [−0.030, 0.055] in the X and Y directions, and [0.080, 0.100] in the Z direction. The possible errors of the axis of the top hammer of the upper hinge beam are [−0.111, 0.135] in the X direction, [−1.180, 1.155] in the Y direction, and [−1.820, 1.915] in the Z direction. (2) The dimensional variation error X1 of the hydraulic cylinder axis of the left hinge beam in the Z direction is compared and calculated by using the one-dimensional dimensional chain. The variation error X1 of the closed ring is [−1.000, 0.780] when the dimensional chain extreme value method is used for analysis, and the variation error X1 of the closed ring is [−0.930, 0.410] when the Monte Carlo method is used for analysis. The calculated result of the Monte Carlo method is less than that of the extreme value method. This is because the calculation assumes that the tolerances of each part follow a normal distribution, which is more in line with the actual production situation and closer to the actual assembly error. (3) When the diameter of the pin adopts the principle of independence, the possible position error of the size of the hydraulic cylinder axis of the left hinge beam in the Z direction is [−1.005, 1.005]. When the diameter of the pin is marked by the inclusion principle, the position error changes to [−0.855, 0.980]. From the comparison of results, the use of different tolerance principles leads to different tolerance analysis results. (4) The Plackett-Burman design (PBD) is used to screen out four highly significant variables, namely, the parallelism tolerance corresponding to variable M1, the dimensional tolerance corresponding to variable M2, and the straightness tolerance corresponding to variables M5 and M7, which have a great impact on the precision of the hinge beam. Conclusions: Based on SDT theory, the three-dimensional tolerance analysis method under different tolerance principles is established for the cubic press, and the possible error variation ranges of the bottom, left and upper hinge beam top hammer axes are calculated respectively. By comparing the errors obtained by the three-dimensional analysis method with those obtained by the one-dimensional dimensional chain method, it is found that the former has a larger error range than the latter, which proves that the three-dimensional analysis model method used in this paper is superior to the one-dimensional tolerance analysis method. At the same time, when the pin diameter is marked with different tolerance principles, the axis error of the hinge beam hydraulic cylinder is calculated, and the error range corresponding to the inclusion principle is smaller than that corresponding to the independent principle. That is to say, when the inclusion principle is applied in the pin diameter marking, the position variation error of the hinge beam hydraulic cylinder axis can be ensured to be smaller, which is more in line with the high-precision requirements of the diamond cubic press. Finally, the four highly significant variables that have great influence on the precision of the hinge beam are selected, providing a theoretical basis for the reasonable distribution of the machining precision of the press hinge beam.
Abstract: Objectives: Polycrystalline diamond compact (PDC) is an ultra-high hardness composite material made from polycrystalline diamond (PCD) and cemented carbide through high temperature and high pressure sintering. PDC is widely used in oil and gas extraction, geothermal development, and coal field drilling. As drilling goes deeper, the formation pressure increases, and the geological rock layers become denser, harder, and more abrasive. Therefore, the comprehensive performance requirements for the drill bit and PDC are increasingly high. The presence of residual thermal stress can significantly weaken the performance of PDC, causing the PCD layer to fracture and detach, which is one of the important factors leading to the premature failure of PDC. Previous research methods for determining the residual thermal stress in PDC have certain limitations. Finite element simulation calculations can effectively compensate for these shortcomings. Therefore, this paper uses the ANSYS Workbench software to calculate and analyze the influence of the thickness ratio of the PCD layer to the cemented carbide layer in PDC and the diameter of PDC on residual thermal stress, providing references for the optimization of PDC design and performance improvement. Methods: ANSYS is one of the most commonly used finite element analysis software, which can effectively integrate multiple disciplines such as structural dynamics, thermodynamics, and fluid dynamics for simulation calculations. Using ANSYS, the model of PDC (assuming that temperature does not affect the physical properties of materials) can be established, and the residual thermal stress of PDC can be analyzed using the thermo-mechanical coupling method (which solves the impact of the temperature field on stress, strain, and displacement in the structure). The specific calculation process in this study is as follows: (1) Select the calculation method for steady-state temperature field and structural mechanics field coupling. (2) Establish the geometric model of PDC. According to the axisymmetric characteristics of PDC, establish its 1/4 structure to save computational space. (3) Define the physical and mechanical properties of the PCD layer and the cemented carbide layer, and then perform mesh division. (4) Set boundary conditions and loads, using the temperature difference as the load, setting the reference temperature including the stress relaxation temperature of PDC, the axisymmetric boundary conditions of the model, as well as the heat convection boundary conditions between the outer surface of PDC and the air. (5) Perform result calculation and analysis. Results: Using the software to simulate the calculation of the residual thermal stress value and distribution during the unloading and cooling process of PDC, the following conclusions can be drawn: (1) The ANSYS simulation calculation shows that when the diameter of PDC is 16 mm and the total thickness is 13 mm, the optimal thickness of the PCD layer is 2.0 mm; (2) When the PCD layer thickness is 2.0 mm, the diameter of the composite piece can be selected as 18 mm, and the residual thermal stress of this specification of PDC is at the best value in the calculated range. When the PCD layer thickness is 3.0 mm, it cannot be decided based on a single residual thermal stress influence; this must rely on the specific application situation and the load condition, with a comprehensive consideration of the influence of the four residual thermal stresses; (3) The point of PDC diameter of 17 mm is one of the many fluctuation points, which may be a critical point. At this time, the radial displacement of the interface far from the center axis of PDC changes abruptly, causing the deflection of the entire PDC to change, and the axial tensile stress at the edge of the interface changes. Conclusion: The finite element calculation method can intuitively and clearly simulate the value and distribution of residual thermal stress during the unloading and cooling process of PDC, and effectively avoid the shortcomings of other experimental tests. It can provide useful ideas and suggestions for the design of PDC by analyzing the influence of the two appearance sizes, composite layer thickness, and diameter on the residual thermal stress of PDC, and drawing relevant conclusions. Based on the outstanding results in the simulation calculation, the conclusions obtained are tested by experiments to ensure the reliability of the final results.
Abstract: Objectives: Compared with Si-based materials, SiC has become an ideal substrate material for chip manufacturing due to its good thermal conductivity, high breakdown electric field strength, and large bandgap width. However, the Mohs hardness of SiC wafer is as high as 9.5, which makes it difficult to grind. The thinning process of SiC single crystal wafers, reducing processing costs, and improving the processing quality of SiC chips have become urgent problems to be solved in the semiconductor industry. This study uses Cu3Sn and Cu6Sn5 intermetallic compounds as bonders to prepare rough and fine grinding diamond wheels for thinning SiC wafers. Methods: On the basis of the research and development of intermetallic compound bonding agent superhard material grinding wheels proposed earlier, the M5/10 diamond grinding blocks and the M1/2 diamond grinding wheel teeth were prepared using raw materials such as diamond, Cu3Sn, Cu6Sn5, graphite, and pore-forming agent through a 450 ℃ hot pressing process. After grinding the upper and lower end faces of the diamond grinding wheel teeth flat, 34 pieces were selected and uniformly bonded to the aluminum substrate tooth groove with universal strong adhesive, and the diamond coarse grinding and fine grinding wheels for silicon carbide wafer thinning were obtained. At the same time, the processing load and wear ratio of the silicon carbide grinding wheel, and the roughness and RTTV (total thickness deviation) of the silicon carbide wafer were systematically characterized. Results: (1)The bending strength and the impact toughness of Cu3Sn material subjected to 450 ℃ hot pressing are 206.6 MPa and 0.45 J/cm2, respectively. The bending strength and the impact toughness of Cu6Sn5 material are 142.0 MPa and 0.31 J/cm2, respectively. (2)With the increase of pore-forming agent amount, the porosity of the grinding wheel teeth significantly increases, while its bending strength rapidly decreases. When the mass fraction of the added pore-forming agent is 20%, the porosity and the bending strength of the grinding wheel teeth are 35.0% and 42.5 MPa, respectively. (3)During the grinding process, the higher the bending strength of the grinding wheel teeth, the greater the holding force of the binder on the diamond, and the grinding wheel is prone to load alarms. However, too low bending strength of grinding wheel teeth will lead to excessive wear of the grinding wheel, easy edge breakage, and even broken teeth. (4) The wear ratio of M5/10 diamond rough grinding and thinning wheel with a mass fraction of 20% pore-forming agent for grinding 6-inch SiC chips reaches 1.0∶5.0, the surface smoothness of SiC chips reaches 0.011 µm, and the fragmentation rate is less than 0.2%. (5) When the mass fraction of the pore-forming agent added is 30%, the porosity and the bending strength of M1/2 fine grinding wheel teeth are 43.0% and 16.2 MPa , respectively. In addition, there are a large number of pores on the surface of the thinning grinding wheel, forming a honeycomb shape, ensuring that the grinding wheel has good chip holding and chip removal effects during the grinding process. At the same time, the wear ratio of the diamond wheel for grinding 6-inch SiC wafer is 1.0∶0.6, the surface smoothness of SiC wafer is 2.076 nm, and the RTTV is 2.55 µm. The process of grinding is smooth with a stable load. Conclusions: Cu3Sn material has high strength and can be used to prepare coarse grinding wheels for thinning SiC wafers. Cu6Sn5 material has good brittleness and can be used to prepare fine grinding wheels for thinning SiC wafers. During the grinding process, the pores in the grinding wheel can play a role in accommodating and removing chips, and can also accommodate failed and detached diamonds, thereby ensuring good surface quality of SiC wafers. The coarse and fine grinding diamond wheels prepared in this paper have obtained good grinding results. However, the diamond used in the grinding wheel for thinning SiC wafers is developing to M0/0.5 at present, which is hoped to achieve the better surface roughness and the lowest surface damage layer of SiC wafers, in order to reduce the processing amount of the CMP process. The follow-up work will further improve the brittleness of Cu6Sn5 material through ceramicization to enhance the sharpness of the grinding wheel, and carry out research on M0/0.5 diamond precision grinding and thinning grinding wheels.
Abstract: Objectives: Vitrified bonded diamond grinding tools are widely used in the machining industry, but the high-temperature resistance of diamond is poor. Therefore, there are high requirements on sintering temperature, flowability, and thermal expansion coefficient of vitrified bond materials. The influence of the content of Al2O3, B2O3, and SiO2 in vitrified bond on its properties is investigated. By changing the content of these three components and comparing the changes in the properties of the bonds, a more suitable vitrified bond for diamond grinding tools is obtained. Methods: Using a ternary phase diagram, the content of Al2O3, B2O3, and SiO2 in the R2O-Al2O3-B2O3-SiO2 bond system is adjusted. Sixteen different formulas were designed to prepare 5 mm × 6 mm × 30 mm sample strips under a pressure of 5 MPa, and dried at 80 ℃ for 12 hours. The refractoriness of each group of bonds was measured using a standard refractory cone, the flowability of the bonds was measured using the plane flow method, and the thermal expansion coefficient of the bonds was determined. According to the refractoriness data determined by each formula, sintering was carried out at a temperature 60 ℃ higher than the refractoriness of the bond. A microcomputer-controlled electronic universal testing machine was used to determine the flexural strength of the bond using the three-point bending method. The microhardness of the bond was measured using a microhardness tester, and the microstructure of the bond was analyzed. Results: From the analysis of the measured performance data, it can be concluded that: (1) B2O3 has the effect of reducing the refractoriness in vitrified bonds, while SiO2 and Al2O3 increase the refractoriness of the bonds. Al2O3 has a greater impact on the refractoriness of the bonds than SiO2. (2) B2O3 has the effect of improving the flowability of bonds, while Al2O3 reduces the flowability of bonds. The thermal expansion coefficient and the flexural strength of the bond will vary depending on the content of Al2O3 and B2O3. When the Al2O3 content in the bond is high, the thermal expansion coefficient of the bond will first decrease and then increase with the increase of B2O3 content, and the flexural strength will first increase and then decrease with the increase of B2O3 content. When the Al2O3 content in the bond is low, the thermal expansion coefficient of the bond will increase with the increase of B2O3 content, and the flexural strength will decrease with the increase of B2O3 content. When the SiO2 content is fixed, the thermal expansion coefficient of the bond will increase with the increase of B2O3 content, and the flexural strength will increase with the increase of Al2O3 content. When the B2O3 content is fixed, the thermal expansion coefficient of the bond will increase with the increase of Al2O3 content, and the flexural strength will increase with the increase of B2O3 content. The influence of each component in the bond on the microhardness change of the bond is SiO2>B2O3>Al2O3. When the molar ratio of Al2O3+B2O3 to Na2O in the bond is less than 1, Al2O3 and B2O3 will combine with oxygen ions in Na2O to form [AlO4] and [BO4], which participate in the network structure of the bond and densify it. Breaking the dense network structure requires higher energy. Therefore, densification of the network structure in the bond can reduce its thermal expansion coefficient and improve its flexural strength and microhardness. When n(Al2O3+B2O3)/n(Na2O)>1, the oxygen ions in Na2O are insufficient, and Al2O3 and B2O3 form [AlO3] and [BO3] triangles, reducing the density of the network structure. The fluffy structure makes the network structure more sensitive to energy, increasing the thermal expansion coefficient of the bond and reducing its flexural strength and microhardness. Conclusions: A ternary phase diagram based on the content of Al2O3, B2O3, and SiO2 in the R2O-Al2O3-B2O3-SiO2 system bond can intuitively reflect the synergistic effect of the three components during sintering. The three components will exhibit different effects in bonds with different contents, and their impact on the performance of the bond will also be different. When designing the formula for vitrified bonds, it is necessary to consider the roles of different components in the bond and their interactions with other components.
Abstract: Objectives: Research on ceramic processing primarily focuses on areas such as single abrasive grinding methods, processing mechanisms, processing efficiency, material removal mechanisms, and surface quality. However, research on ZrO2 ceramic cutting processing is relatively insufficient. Therefore, the 3D cutting process of ZrO2 ceramic workpieces was numerically simulated using the finite element simulation method. The study discusses the mechanism of chip removal, the dynamic change and distribution of stress, and the evolution law of cutting force under various cutting conditions. Methods: The 3D cutting process of ZrO2 ceramic workpieces, under different machining parameters and tool parameters, was numerically simulated using the finite element simulation method. The cutting forces under various feed speeds and cutting depths were compared to explore the failure modes and material removal mechanisms of ZrO2 ceramic during the cutting process. Results: The hard contact behavior between the cutting tool and the workpiece significantly affects the material removal process, leading to failure modes such as chip collapse, material cracking, and crack propagation. When the cutting depth is 200 μm or 250 μm, numerous cracks appear at the end edge of the workpiece and expand in the vertical cutting direction, resulting in significant fragmentation at the edge. An increase in cutting speed will causes fluctuations in stress and cutting force, but overall, there is no significant change in cutting performance. The radius of the cutting edge affects the formation of cracks in the initial cutting stage. As the edge radius increases, the length of the crack at the front end of the tool shortens, though the impact on cutting force is not significant. A negative tool rake angle during cutting does not induce cracks in the workpiece, and it leads to better machining quality. In addition, when the tool rake angle is 0 °, the maximum cutting force increases rapidly, but the cutting force variation is not obvious with increasing rake angle. Conclusions: As the cutting depth increases, the stress layer on the tool surface gradually expands from the tip to the front and rear cutting surfaces, and gradually increases. As the cutting depth increases, local cracks form at the cutting end of the workpiece and propagate downward. The position of maximum stress on the front cutting surface of the tool gradually increases with the increase in edge radius. However, the influence of the edge radius on the cutting force is relatively small. When cutting ZrO2 ceramics with a tool featuring a negative rake angle, no internal cracks are caused, and good machining quality can be achieved.
Abstract: Objectives: Electroplated diamond wire saws are widely used in the field of slicing hard and brittle materials such as monocrystalline silicon and sapphire. Cutting fluid should give full play to its role in the sawing process, which is conducive to the improvement of wafer quality. As the size of the wafer increases and the diameter of the wire saw decreases, the kerf in the sawing process becomes deeper and narrower, and the cutting fluid cannot enter the kerf in large quantities, resulting in worse lubrication and cooling effects during the sawing process, which leads to the decline of the surface quality of the wafer. Based on computational fluid dynamics (CFD) numerical simulation methods, the cutting fluid flow field in the cutting seam of the diamond wire saw was analyzed and studied. Methods: In this paper, based on CFD numerical simulation methods, the cutting fluid flow field in the sawing seam of the diamond wire saw is analyzed and studied. Firstly, according to the actual situation of the diamond wire saw cutting process, a 3D simulation geometric model is established based on the liquid supply mode, where cutting fluid flows along the sawing wire and is brought into the sawing area by the motion of the sawing wire. Heat transfer is not considered in this study, and the cutting fluid is assumed to be a viscous incompressible fluid. The governing equations of fluid flow include the continuity equation and the momentum equation. It is found from the equations that the main factors affecting the flow field distribution of cutting fluid in the kerf are wire speed and cutting fluid density. By calculating Reynolds number and Weber number, the fluid model studied in this paper is selected as the Transition SST model. The VOF method is determined to characterize the fluid state of cutting fluid in the saw joint, and the CSF model is introduced into the VOF method to characterize the influence of surface tension. Considering the influence of physical properties of cutting fluid, the density, viscosity, surface tension, and wall contact angle of cutting fluid are measured experimentally. The momentum equation is solved by a pressure-based solver, the continuity equation is solved by implicit time discretization, and the PISO method is used for pressure-velocity coupling. Result: With the increase of chip size and the decrease of wire saw diameter, the size of the saw seam is getting smaller and smaller. The main fluid entering the saw seam is shear flow, and the main factor affecting the fluid motion state is the wire speed. Under the condition of small-size sawing, when the wire speed is low (vw≤25 m/s), both the contact area and the non-contact area of the saw wire in the sawing joint are not completely filled with liquid, and the liquid volume fraction in the contact area is < 100%, with an air layer in the area. With the increase of wire speed, more and more cutting fluid enters the sawing joint. With the increase of wire speed, more and more cutting fluid enters the saw seam. When vw>25 m/s, both the contact area and the non-contact area are filled with liquid. The cutting fluid pressure in the saw seam increases with the increase of wire speed on both the contact area side and the non-contact area side, and the pressure difference on both sides also increases generally. The pressure distribution on both sides becomes more stable. After both sides of the saw seam are filled with liquid, the pressure on one side of the contact area is about 0.1790 MPa, and the pressure on one side of the non-contact area is about 0.1590 MPa. With the gradual reduction of the viscosity and surface tension of the cutting fluid, the cutting fluid gradually fills the saw joint. Howver, when the viscosity and surface tension of the cutting fluid are too small, the cutting fluid entering the saw joint will tend to decrease. The cutting fluid pressure in the saw seam increases with the decrease of the cutting fluid viscosity and surface tension in both the contact area and the non-contact area, and the pressure distribution becomes more stable. However, when the viscosity and the surface tension are too small, the pressure will also fluctuate. Under the physical properties of the cutting fluid C, with a density of 872.5 kg·m−3, viscosity of 1.15 mPa·s and surface tension of 34.02 mN·m−1, the pressure distribution of the cutting fluid on the contact area side and the non-contact area side is more stable. The maximum pressure on the contact area side is about 0.0169 MPa, and the maximum pressure on the non-contact area side is about 0.0132 MPa. Conclusions: (1) Under small sawing sizes, when the wire speed is low, the cutting fluid is difficult to fully enter the sawing area to play its role. With the increase of the wire speed (vw>25 m/s), the contact area and non-contact area between the saw wire and the workpiece are gradually filled with liquid, and the cutting fluid pressure and pressure difference between the contact area and the non-contact area show an overall increasing trend. When the contact area and non-contact area are full of cutting fluid, the cutting fluid pressure distribution in the saw joint is relatively stable, with the pressure in the contact area being about 0.1790 MPa and the pressure in the non-contact area being about 0.1590 MPa. (2) The reduction of liquid viscosity and surface tension within a certain range is conducive to ensuring the relative saturation and stability of the cutting fluid in the saw joint, and at the same time, it can make the pressure distribution of the cutting fluid in the saw joint more stable. A comprehensive comparison of the physical properties of the 5 groups of cutting fluids shows that the physical properties of the cutting fluid C during the diamond line saw cutting process are more conducive to its entry into the saw joint.
Abstract: Objectives: The existing literature on numerical simulation of cutters rarely considers the effect of wear height on the temperature and cutting load of cutters. However, the deterioration of force and the aggravation of thermal wear after the wear of polycrystalline diamond composite (PDC) cutters lead to their rapid failure. Therefore, it is particularly necessary to study the change of cutting load and the law of heat generation of worn cutters to extend their service life. Methods: Based on elastoplastic mechanics and rock mechanics, a 3D dynamic rotational simulation model of worn teeth is established with the Drucker-Prager criterion as the rock constitutive model. The stress state and temperature rise amplitude of cutting teeth under different wear heights, cutting depths, and front inclination angles are analyzed by numerical simulation. Results: (1) Influence of wear height on cutting load: Under simulated conditions (front inclination 15°, cutting depth 1.5 mm), the size and the fluctuation degree of cutting load increase with the increase of wear height when the wear height is 0−1.5 mm, and decrease slightly when the wear height is larger than 1.5 mm. In terms of tangential force, the cutter with a wear height of 1.5 mm is subjected to the largest tangential force, but when the wear height is 2.0 mm, the tangential force is reduced. In terms of axial force, the axial force of worn teeth is higher than that of unworn teeth. When the wear height is 0−1.5 mm, the axial force gradually increases with the increase of wear height. When the wear height is 1.5 mm, the axial force reaches its maximum, and when the wear height is larger than 1.5 mm, the axial force decreases. The axial force of the cutter with a wear height of 1.0 mm and wear height of 2.0 mm is exactly 1.2 times that of the unworn tooth, and the axial force of the cutter with a wear height of 1.5 mm is 1.3 times that of the unworn tooth. (2) Influence of cutting depth on cutting load: Under simulated conditions (wear height 1.0 mm, front inclination angle 15°), tangential force and axial force gradually increase with the increase of cutting depth, and the degree of fluctuation is more intense. In terms of tangential force, the tangential force of the worn tooth with the cutting depth of 2.0 mm is 1.9 times that of the worn tooth with the cutting depth of 1.0 mm, and the increase is larger. The tangential force of the worn tooth with the cutting depth of 1.5 mm is only 25% higher than that of the worn tooth with the cutting depth of 1.0 mm, and the increase is small. In terms of axial force, with the increase of cutting depth, the increase in axial force is relatively balanced. (3) Influence of front inclination angle on cutting load: Under simulated conditions (wear height 1.0 mm, cutting depth 1.5 mm), the cutting load of worn teeth gradually increases with the increase of front inclination angle, with the tangential force increasing by 28% and the axial force increasing by 32%. When the front angle is 10°, the fluctuation of the cutting load is more severe than at other time with 15° and 20°. (4) Influence of wear height on cutting heat: according to the temperature cloud map of the cutter, because the cutter rotates around the central axis to break rock, the linear speed of the cutting edge differs, and the temperature on the side away from the central axis will be higher than that on the side near the central axis. With the increase of wear degree, the temperature rise of the cutter becomes more significant, and the high-temperature area is concentrated in the cutting-cutter contact area, where plastic deformation and frictional heat generation are concentrated. The temperature change curve can be divided into three stages: rising period, transitional period, and stable period. With the passage of time, the temperature of the cutter continues to rise, and the temperature rise rate in the rising period is greater than in the transitional period, tending to flatten after entering the stable period. In the process of rock breaking, the temperature rise of worn teeth is much higher than that of unworn teeth, with a temperature increase of 54%−103%. Conclusions: The force on a cutter with excessive wear is more complex and variable, increasing the risk of fatigue failure. In terms of tooth layout, it can be considered to place the auxiliary cutting unit behind the main cutting unit composite sheet and make its exposure height lower than the composite sheet, which can effectively reduce the load on the main cutting gear and reduce the probability of overload damage to the cutting gear. The cutting load of the worn teeth increases with the increase of the front angle. Considering the fluctuation of cutting efficiency and load, the front angle should be controlled at 15°−20° as far as possible, which is beneficial to prolong the service life of the cutting teeth. After cutter wear, its ability to break rock is weakened, the rock pre-crushing area is reduced, and the way of cutting the rock gradually transitions from shear failure to extrusion failure, greatly reducing the rock-breaking efficiency of the cutter. In the process of cutting rock breaking, the temperature rise of the worn teeth is much higher than that of the unworn teeth, and the temperature rise increases with the increase of wear degree. Thus, the thermal wear of the cutting teeth will continue to intensify after wear, accelerating the wear and failure of the cutting teeth. In the subsequent cutting process, cutter of wear-resistant and high-temperature-resistant materials can be selected to reduce the weight on the bit and the speed of drilling while increasing the water power of the pump, effectively inhibiting thermal wear.
Abstract: Objectives: Bone tissue grinding is one of the common and basic applications in orthopedic surgery clinics. The grinding process is energy-intensive and generates a lot of grinding heat. The accumulation of this heat may cause thermal damage to biological tissues. This paper presents experimental research to investigate the bone-grinding heat and the cooling method. Methods: The combined influence of nozzle position and feed direction on the cooling effect of bone grinding under cryogenic spray cooling conditions is experimentally investigated. A bone grinding platform with three-dimensional motion, as well as a cryogenic spray generation device, is designed and constructed. A spherical diamond grinding head with a diameter of 4 mm and a grit size of #150 is utilized. Fresh bovine cortical bone is used as the processing sample. The temperature at the nozzle outlet is 13 ℃, and the flow rate valve regulates the coolant flow rate to 400 mL/h. A three-dimensional force transducer (DJSW-40, China) is connected to a data acquisition system, which captures the forces applied to the bone sample along the X, Y, and Z directions at a frequency of 100 Hz. Simultaneously, a 0.1 mm diameter type K thermocouple (Omega Inc., TT-K-36) is embedded inside the bone sample to measure the grinding temperature in real-time. Three different nozzle arrangements were designed: above, in front of, and to the side of the abrasive tool, with the nozzles 10 mm away from the spray surface. Six sets of experiments (3×2) were designed using three nozzle orientations and two feeding directions. Each set of experiments was repeated three times to study the cooling effect of the spray under the combined influence of nozzle orientation and feed direction. Results: (1) During bone grinding, the abrasive tool is subjected to three orthogonal directional forces, namely FX (the tangential grinding force used for removing material), FY (the axial grinding force, representing the resistance of the abrasive tool during its feed), and FZ (the normal grinding force, which serves as the support force of the workpiece on the abrasive tool). For forward feed, the average values of the individual forces are: FX = 0.37 N, FY = -0.72 N, FZ = 1.38 N. For backward feed, FX = 0.46 N, FY = 0.78 N, FZ = 1.67 N. Since the grinding tool remains in the same rotational direction, the tangential force FX is consistently positive. For forward/backward feed, the axial force FY is in the -Y and +Y directions respectively, thus the sign of the FY value changes. When feeding forward/backward, the tangential force (FX) is 0.37 N and 0.46 N, respectively, which are relatively similar to each other, in accordance with the grinding theory. The power consumed for grinding is approximately 1.6 W and 1.9 W for forward and backward feed, respectively. (2) The nerve tissue is more heat-sensitive than bone tissue. Taking the human body's 37 ℃ as the base temperature, the threshold for the occurrence of thermal injury is 43 ℃, so the temperature rise threshold for thermal injury of nerve tissue is 6 ℃. In our experiment, the maximum temperature rise of bone under low-temperature spray cooling was lower than 4 ℃, indicating that the cooling method is effective. The effect of the nozzle arrangement was investigated under a fixed forward or backward feeding direction. When the abrasive tool is fed forward, the cooling of the thermocouple under the front nozzle is obvious. This is because, in addition to the contact arc area between the abrasive tool and the bone sample, a portion of the coolant from the front nozzle is sprayed onto the bone sample surface, resulting in a pre-cooling effect within the bone. When the abrasive tool is fed backward, the grinding temperature is lowest when the nozzle is placed above. For the different nozzle orientations, the side nozzles are in a perpendicular plane to the feed direction (Y-direction) of the grinding tool, so the feed direction has the least influence on the grinding temperature. The upper and front nozzles are in the same plane as the feed direction of the abrasive tool, so the influence of the feed direction is more significant. Conclusions: (1) The average tangential grinding force is 0.42 N, axial grinding force is 0.75 N, normal grinding force is 1.53 N, and the average power consumed by grinding is approximately 1.75 W when bone grinding is performed at a depth of 0.5 mm using a spherical diamond abrasive tool with a diameter of 4 mm. (2) Under the cooling effect of the cryogenic spray, the maximum temperature rise of grinding is less than 4 ℃, which can effectively prevent the occurrence of thermal damage in biological tissues. The temperatures of the two thermocouples in the same set of experiments were more consistent when the nozzle was placed above or side, while there was a significant difference in the temperatures of the two thermocouples when the nozzle was placed in front. This indicates that the cooling effect is more uniform when the nozzle is placed above and to the side. (3) The coupling of the nozzle arrangement and the feeding mode has a greater impact on the grinding temperature. When the nozzle is placed on top, it is favorable to backward feeding; when the nozzle is placed in front, it is conducive to forward feeding; and when the nozzle is placed on the side, there is no significant difference in the temperature between forward and backward feeding.
Abstract: Objectives: Aero engine blades are important components in engines, and the machining accuracy of the blade edge directly affects the aerodynamic performance of the blade. Improving the surface roughness and the profile accuracy of the blade edge are crucial to improving the service life and the performance of the engine. However, the curvature radius of the blade edge surface varies greatly to even less than 0.05 mm, which puts higher requirements on processing equipment and technology. Therefore, the polishing process of blade edges is studied and a fixed resin diamond elastic polishing wheel adapting to the shape of the blade edge is developed to explore its feasibility on a 6R robot polishing platform when polishing blade edges. Methods: The fixed resin diamond elastic polishing wheel is developed based on the characteristics of small curvature radius and complex surface shape of the blade edge, and a robot polishing platform is built to study the polishing process of Ti alloy blade edges. Firstly, by combining UG secondary development with robot kinematics, the polishing path of the wheel based on the robot platform for polishing blade edges is planned. Secondly, the orthogonal experimental method is used to explore the influences of four main process parameters, namely spindle speed (A), feed rate (B), machining pressure (C), and abrasive particle size (D), on the surface roughness and contour of the blade edge. The optimal combination of process parameters is then obtained. Finally, the titanium alloy blade edge workpiece is polished using the optimal parameter combination, and the surface roughness and the contour of the workpiece after polishing are measured to determine whether the polishing quality of the workpiece meets the requirements for use. Results: The orthogonal experiments are conducted on titanium alloy blade edge polishing using the fixed resin diamond elastic polishing wheel on the 6R robot polishing platform. The experimental data show that: (1) Among the four process parameters A, B, C and D, B has the greatest impact on the blade edge profile with a range R1 of 0.015. The second greatest influences are from A and C, and the least influence is from D. The optimal combination of process parameters is A2B1C2D3, that is, the spindle speed is 700 r/min, the feed speed is 6 mm/min, the processing pressure is 4 N, and the abrasive particle size is 10~14 μm. (2) B has the greatest effect on the surface roughness of the blade edge, with its range R2 being 0.136, which is much higher than that of other parameters. The second greatest influences are from D and A, and the least influence is from C. The optimal combination of process parameters is A3B1C2D3, that is, the spindle speed is 800 r/min, the feed speed is 6 mm/min, the processing pressure is 4 N, and the abrasive particle size is 10~14 μm. Conclusions: A new type of resin diamond elastic polishing wheel is innovatively designed by combining fixed abrasive technology and elastic polishing technology, which is suitable for the characteristics of large curvature changes and complex surfaces of the blade edge. It is used for orthogonal experiments of blade edge polishing on the 6R robot polishing platform. The experimental results show that the designed and developed elastic polishing wheel is suitable for polishing the edges of titanium alloy blades, and the surface roughness and profile accuracy of the processed edges can meet the requirements for use. At the same time, the optimized process parameter combination for polishing the edge of titanium alloy blades is A3B1C2D3, which includes a spindle speed of 800 r/min, a feed rate of 6 mm/min, a processing pressure of 4 N, and an abrasive particle size of 10～14 μm. Under these parameters, the overall effect of blade edge polishing is the best, with the surface roughness Ra decreasing from the initial 1.165 μm to 0.213 μm, and the profile decreasing from the initial 0.048 mm to 0.016 mm.
Abstract: Objectives: In recent years, cerium-based rare earth polishing liquids have been widely used in the field of chemical mechanical polishing (CMP) of glass and other materials due to their excellent selectivity and good polishing efficiency, but their polishing performance needs to be further improved. Using Baotou mixed rare earth ore as the raw material and other additives as auxiliary materials, the LaCePr rare earth CMP polishing solution with good comprehensive performance was prepared through a complex process. The microstructure, the element distribution, and phases were studied, and specific polishing experiments were conducted to evaluate its polishing performance. Methods: The LaCePr chlorination solution was prepared using the product of Baotou mixed rare earth ore, which underwent concentrated sulfuric acid enhanced roasting, water leaching, neutralization and impurity removal, P507 extraction transformation and grading. The mixture of ammonium bicarbonate and ammonia water was used as a precipitant, hydrofluoric acid was used as a fluorinating agent, and sodium polyacrylate, sodium hexametaphosphate, sodium hydroxide and other additives were added. The LaCePr rare earth CMP polishing solution samples were prepared through processes such as co-flow precipitation, fluorination, high-temperature roasting, introduction of additives, slurry mixing, and wet ball milling. Subsequently, the macroscopic structure of the prepared polishing solution was observed, and the elemental distribution in the sample was measured using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The solid polishing powder sample of the LaCePr rare earth polishing solution after air drying was analyzed using X-ray diffraction (XRD). The CMP polishing performances of the prepared LaCePr rare earth polishing solution were tested, and the polishing effect of the workpiece was evaluated using the planar precision polishing machine and the optical 3D surface profilometer. Results: (1) The morphology of the solid polishing powder after air-drying of the polishing liquid consists of irregular polygonal spherical grains tightly aggregated, which mainly shows that the fine particles are agglomerated together. In addition, there are no coarse particles in the whole cluster, indicating that the introduction of F and doping of Pr have a positive effect on the lattice distortion of CeO2. (2) The microstructure and the element distribution diagram of the solid polishing powder show that the solid solution second-phase particles appear around the grain boundaries of individual particles, indicating that the doped La and Pr elements mainly enter the CeO2 lattice in a solid-solution manner. The La, Ce, Pr and O elements are uniformly distributed, confirming that the introduction of the F element can play a role in grain refinement. (3) In addition to the characteristic peaks of the CeO2 phase, the diffraction peaks of LaOF, Pr6O11, LaF3, PrOF and other phases are also observed in the rare earth polishing solution sample, indicating that the doped La, Pr and F elements enter the CeO2 lattice in the form of a solid solution of solute atoms. The face-centered cubic Pr6O11 structure is the same as that of CeO2, so it can exert a synergistic polishing effect together with CeO2. (4) The initial polishing ability of the LaCe rare earth polishing solution is 182.6 nm/min. After polishing for 40, 60, 80 and 120 minutes, the polishing abilities of the LaCe polishing solution are 199.3, 199.9, 193.8 and 158.2 nm/min, respectively. The initial polishing ability of the newly prepared LaCePr rare earth polishing solution is 203.4 nm/min. After polishing for 40, 60, 80, and 120 minutes, the polishing abilities of the LaCePr polishing solution are 219.7, 214.7, 206.3 and 189.8 nm/min, respectively. (5) The surface roughness Sa of the glass after five CMP cycles with the LaCe polishing solution is 0.659 nm, while the surface roughness Sa of the glass after five CMP cycles with the LaCePr polishing solution is 0.668 nm. Conclusions: By using LaCePr rare earth chloride solution, the LaCePr rare earth polishing solution can be successfully prepared through processes such as precipitation, fluorination, high-temperature calcination, additive blending, and wet ball milling. The entire process of the preparing polishing solution has achieved zero wastewater discharge, which is a green polishing solution preparation process. After air drying, the LaCePr rare earth polishing solution, the medium particles in the sample are well-formed and evenly distributed. The doped La, Pr and F elements all enter the CeO2 lattice through solute atom solid solution. The cubic fluorite structure of CeO2, the tetragonal structure of LaOF, and the face-centered cubic structure of Pr6O11 in the LaCePr rare earth polishing solution exhibit a synergistic polishing effect. After 120 minutes of cumulative polishing of H-K9L optical glass, the maximum polishing rate of the LaCe polishing solution is 199.9 nm/min, while the maximum polishing rate of the LaCePr polishing solution can reach 219.7 nm/min. The polishing quality of H-K9L glass is basically the same after polishing with the two kinds of polishing solutions, and the surface roughness Sa decreases from the initial 1.123 nm to 0.659 nm and 0.668 nm, respectively. Therefore, the comprehensive properties of the prepared LaCePr CMP polishing liquid are better.
Abstract: Objectives: With the development of modern processing technology, heat accumulation has become an urgent processing problem that needs to be solved. A heat pipe is a heat exchange element that efficiently transfers heat through the gas-liquid phase change of the working fluid inside the pipe. Gravity heat pipe have advantages such as simple structure, stable operation, and low cost, and are widely used in various heat exchange scenarios in industrial production. They have played a significant role in energy conservation, the development and utilization of new energy, and in strengthening heat exchange during processing. This article prensents experimental research on diamond nanofluids, exploring the influence of different parameters on the heat transfer performance of diamond nanofluid gravity heat pipes, laying a foundation for the research and application of heat pipe technology in heat dissipation during machining processes such as drilling, milling, and grinding. Methods: The evaporation section is heated using a DC power supply and thermal resistance wire. K-type thermocouples and temperature acquisition cards are used to record the temperature of the evaporation and condensation sections of the gravity heat pipe. The influence of heating power, filling rate, nanofluid concentration, and nanoparticle size on the heat transfer performance of the gravity heat pipe is analyzed using thermal resistance R as an indicator. Results: The heat transfer performance of gravity heat pipes is investigated under a power range of 3-18 W, while maintaining a filling rate of 20% and a nanoparticle concentration of 1%. The results show that as the heating power increases, the temperatures of the evaporation and the condensation sections gradually increase, while the rise time gradually shortenes. The temperature difference between the evaporation and condensation sections shows a decreasing trend. When the heating power increases for the same concentration and filling rate of nanoparticles, the total thermal resistance shows a decreasing trend, but the magnitude of the decrease continues to decrease. Keeping the concentration of nanoparticles at 2% and the heating power at 6 W, the heat transfer performance of gravity heat pipes is investigated under conditions of filling rates of 8%, 14%, 20%, and 26%. The results show that the overall temperature of the 20 nm diamond nanofluid is higher than those of other filling rates at a 20% filling rate, while the overall temperature at a 26% filling rate is lower than at other filling rates. The overall temperature at a 26% filling rate is higher than at other filling rates. With the same mass fraction and heating power, as the filling rate increases, the total thermal resistance shows a trend of first decreasing and then increasing, with the minimum value of the total thermal resistance appearing at a filling rate of 14%. By maintaining a filling rate of 26% and a heating power of 12 W, the heat transfer performance of gravity heat pipes under 0.5%, 1.0%, 1.5%, and 2.0% mass fraction conditions is investigated. The results show that the overall temperature of 20 nm diamond nanofluid heat pipes is the highest at a 1% mass fraction, while the overall temperature is lower at a 2.0% mass fraction. The hot-end temperature of 50 nm diamond nanofluid heat pipes is the highest at a 1.5% mass fraction, and the cold-end temperature is the lowest. At a mass fraction of 2.0%, there is a situation where the hot-end temperature is lower and the cold-end temperature is higher. With the same filling rate and heating power, as the mass fraction increases, the total thermal resistance first increases and then decreases. At a mass fraction of 2.0%, the minimum total thermal resistance will appears. In addition, for diamond nanofluids with different particle sizes, there is a trend of heat transfer capacity decreasing first and then improving with increasing mass fraction. Maintaining a filling rate of 14% and a mass fraction of 2.0%, the heat transfer performance of gravity heat pipes with particle sizes of 20 nm and 50 nm was investigated. The total thermal resistance of 50 nm diamond nanofluid gravity heat pipes was always lower than that of 20 nm diamond nanofluid gravity heat pipes. However, as the heating power increases, the advantage of 50 nm diamond nanofluid gravity heat pipes tends to weaken. Maintaining a liquid filling rate of 14% and a mass fraction of 2.0%, the heat transfer performance of gravity heat pipes with and without a liquid absorbing core was investigated. The total thermal resistance of gravity heat pipes with suction cores is lower than that of heat pipes without suction cores, but as the heating power increases, the advantage tends to weaken. Conclusions: When the mass fraction is 2.0%, gravity heat pipes have the best heat transfer performance, with a total thermal resistance increase of approximately 28.4%-64.7% compared to the maximum value. When the filling rate is 14%, the heat transfer performance is the best, and the total thermal resistance decreases by about 6.1%-8.5% compared to the maximum value. When using diamond nanofluids with a particle size of 50 nm, the overall heat transfer performance of gravity heat pipes is better than that of 20 nm. When the heating power of the power supply increases, the heat exchange performance also improves. When using a gravity heat pipe with a liquid absorbing core, its overall heat transfer performance is better than that of a gravity heat pipe without a liquid absorbing core.
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