A double-gradient PcBN compact and a 3D printing preparation method thereof

Abstract

The application discloses a double-gradient PcBN composite sheet and a 3D printing preparation method thereof, the PcBN composite sheet is divided into a PcBN layer, a gradient transition layer and a gradient cemented carbide base from top to bottom along an axial direction, in the gradient transition layer, the content of the PcBN gradually decreases and the content of the cemented carbide gradually increases from top to bottom along the axial direction, and in the gradient cemented carbide base, the content of cobalt changes in a gradient mode from the center to the outside along the radial direction, the PcBN composite sheet is obtained through 3D printing and high-temperature and high-pressure synthesis, the application effectively relieves the interface thermal stress caused by the difference in the thermal expansion coefficient between the PcBN working layer and the cemented carbide base by introducing the gradient transition layer, the impact toughness of the composite sheet is significantly improved by adopting the gradient structure cemented carbide base, the 3D printing technology is combined with the high-temperature and high-pressure synthesis technology, and not only the limitation of the traditional PcBN composite sheet preparation process is broken through, but also high efficiency and low cost preparation are realized.

Description

Technical Field

[0001] This invention belongs to the field of superhard material preparation technology, specifically relating to a dual-gradient PcBN composite sheet and its 3D printing preparation method. Background Technology

[0002] Polycrystalline cubic boron nitride (PcBN) composite sheets are widely used in the machining of iron-based composite materials due to their extremely high hardness, excellent thermal stability, and good chemical inertness. Conventional PcBN composite sheets are typically formed by bonding a PcBN working layer to a cemented carbide substrate under high temperature and high pressure conditions. However, due to significant differences in physical properties such as thermal expansion coefficient and elastic modulus between PcBN and the cemented carbide substrate, large residual thermal stress is easily generated in the interface region during the cooling process after high-temperature and high-pressure synthesis. This leads to cracking or delamination failure of the PcBN composite sheet under alternating hot and cold conditions. Furthermore, the poor toughness of the cemented carbide substrate makes it prone to matrix fracture of the PcBN layer, severely limiting its service life and reliability. Traditional manufacturing processes often involve direct powder stacking followed by high-temperature and high-pressure sintering, which limits the freedom of structural design and makes it difficult to construct an ideal transition layer structure to effectively alleviate interface stress and improve the impact toughness of the cemented carbide substrate.

[0003] The development of additive manufacturing technology has provided a new technological path for the preparation of complex structural materials. Among them, fused deposition modeling (FDM) technology has shown good application prospects in the field of ceramic matrix composite molding due to its advantages such as low equipment cost, wide material adaptability, and simple operation. Introducing FDM technology into the preparation process of PcBN composite sheets is expected to break through the limitations of traditional powder forming processes, realize the gradient change of material composition between PcBN and cemented carbide substrate, thereby optimizing the interface structure, alleviating thermal stress, and improving toughness matching.

[0004] Therefore, developing a dual-gradient PcBN composite sheet with low interfacial residual stress and high impact toughness, and its efficient and low-cost preparation process, is of great significance for overcoming the performance bottleneck of existing PcBN composite sheets. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the first objective of this invention is to provide a PcBN composite sheet with a dual-gradient structure. The PcBN composite sheet of this invention features a dual gradient: firstly, a gradient transition layer between the working layer and the substrate; and secondly, a hard alloy substrate with a gradient distribution of cobalt content. Through the synergy of these dual gradients, the interface structure is significantly optimized, thermal stress is alleviated, and toughness matching is improved.

[0006] The second objective of this invention is to provide a method for preparing a PcBN composite sheet with a dual-gradient structure. The preparation method of this invention uses multi-nozzle FDM 3D printing technology. According to the gradient change requirements of the material composition of each layer, different linear printing materials are switched layer by layer to achieve precise and controllable forming of the composition from the PcBN working layer to the gradient transition layer and then to the gradient cemented carbide substrate. This method breaks through the process limitations of traditional powder stacking assembly, which can not only optimize the comprehensive mechanical properties of the product, but also improve production efficiency and effectively control production costs.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] The present invention discloses a dual-gradient PcBN composite sheet, wherein the PcBN composite sheet is divided into a PcBN layer, a gradient transition layer, and a gradient cemented carbide substrate along the axial direction from top to bottom. In the gradient transition layer, the PcBN content gradually decreases and the cemented carbide content gradually increases along the axial direction from top to bottom. In the gradient cemented carbide substrate, the cobalt content changes in a gradient from the center to the radial direction outward.

[0009] The PcBN composite sheet provided by this invention features a transition layer with a gradient of material composition along the thickness direction between the working layer and the substrate. This effectively alleviates the residual thermal stress caused by the difference in thermal expansion coefficients between PcBN and cemented carbide. Simultaneously, the cemented carbide substrate with a gradient cobalt content, where tungsten carbide particles act as the hard phase, forms a high-hardness, high-wear-resistant layer after sintering with cobalt, sufficient to maintain substrate strength. The cobalt content, as a metallic binder, increases radially, providing plastic deformation capacity to absorb impact energy and hinder crack propagation. This significantly improves the toughness of the substrate while maintaining its strength. Furthermore, there is no obvious interface boundary between the gradient cemented carbide substrate and the gradient transition layer, making it difficult for cracks to propagate along a specific plane. The toughness of the gradient substrate gradually decreases from the inside to the outside, corresponding to the strength gradient of the transition layer, resulting in higher damage tolerance at the bonding site and reducing the likelihood of brittle peeling. This synergistically solves problems such as PcBN layer detachment, cracking, chipping, and cemented carbide substrate fracture that occur in PcBN composite sheets under alternating hot and cold conditions, significantly extending the service life of the composite sheet.

[0010] In a preferred embodiment, the gradient transition layer is divided into N layers along the thickness direction, where N is 2 to 10, preferably 4 to 6, and each layer is composed of PcBN and cemented carbide.

[0011] In a further preferred embodiment, in the gradient transition layer, the volume fraction of PcBN in the top layer is 75-95%, and the volume fraction of cemented carbide in the top layer is 15-30%. Then, from the second-to-last layer to the bottom layer, based on the content of the top layer, the volume fraction of PcBN decreases by 10-20% layer by layer, and the volume fraction of cemented carbide increases by 10-20% layer by layer.

[0012] In a further preferred embodiment, the cemented carbide in the gradient transition layer is Co-WC, with a volume fraction of Co of 5-15% and a volume fraction of WC of 85-95%.

[0013] In a preferred embodiment, the cemented carbide in the gradient cemented carbide substrate is Co-WC, wherein the volume fraction of Co is 5-20% and the volume fraction of WC is 80-95%.

[0014] In a preferred embodiment, the gradient cemented carbide substrate is divided into M concentric and coaxial layers along the radial direction, where M is 2 to 6, preferably 3 to 4. The substrate includes a concentric cylindrical core at the center and M-1 annular cylindrical layers that are stacked sequentially from the inside to the outside around the concentric cylindrical core. In the concentric cylindrical core, the volume fraction of Co is 15 to 20%, and the volume fraction of WC is 80 to 85%. Then, from the first annular cylindrical layer to the M-1th annular cylindrical layer, based on the composition of the concentric cylindrical core, the volume fraction of Co decreases by 3 to 8% layer by layer, and the volume fraction of WC increases by 3 to 8% layer by layer.

[0015] Experiments revealed that the volume fraction of Co gradually decreases from the center outwards, while the volume fraction of WC hard phase gradually increases. This means that the wear resistance gradually improves from the center outwards, while the toughness gradually decreases. The outer layer provides wear resistance, while the inner layer provides impact toughness, achieving the dual characteristics of toughness and wear resistance in gradient cemented carbide. Excessive layering increases fabrication complexity; too many interfaces can accumulate microscopic defects, becoming potential crack initiation points; and an excessive number of layers can lead to decreased interlayer bonding. Furthermore, differences in shrinkage between layers during sintering may cause microcracks or deformation.

[0016] In a further preferred embodiment, the diameter of the concentric cylindrical core in the gradient cemented carbide substrate accounts for 1 / 3 to 1 / 2 of the substrate's diameter, while the remaining annular cylindrical layers have equal radial thickness distribution. This distribution method results in optimal performance for the gradient cemented carbide substrate. If the core diameter is too small, it weakens the toughness and buffering capacity; if the core is too large, the wear-resistant layer becomes too thin. Uneven thickness distribution among layers or uneven thickness of the outer layers can lead to abrupt changes in composition, stress concentration, or sintering deformation, thereby causing annular cracks, spalling, or elliptical distortion, affecting the overall performance of the substrate.

[0017] Further preferred, the composition of the cemented carbide in the gradient transition layer is consistent with that of the outermost layer of the gradient cemented carbide substrate. Experiments have shown that selecting a cemented carbide composition with a lower Co content in the gradient transition layer can achieve good overall cutting performance.

[0018] This invention also provides a method for preparing a dual-gradient PcBN composite sheet. Based on the composition of the gradient cemented carbide substrate, M parts of cemented carbide powder in different proportions are prepared. Based on the composition of the gradient transition layer, cBN powder and cemented carbide powder are mixed to obtain N parts of mixed powder in different proportions. Then, M parts of cemented carbide powder, N parts of mixed powder, and cBN powder are respectively mixed with a molding agent, granulated, and drawn into N+M+1 groups of filaments. The N+M+1 groups of filaments are printed using a 3D printer to obtain a green blank. The green blank is then degreased and sintered under high temperature and high pressure to obtain a dual-gradient PcBN composite sheet.

[0019] In a preferred embodiment, the particle size of the cemented carbide powder is ≤30μm, and the particle size of the cBN powder is 10~50μm. Experiments have shown that controlling the particle sizes of both the cemented carbide powder and cBN powder within this range yields optimal performance. If the cBN powder particle size is too small, it is prone to agglomeration and excessively high filament viscosity, leading to printing blockage and abnormal grain growth during sintering. If the cBN particle size is too large, the particle strength is low, and the interfacial bonding is poor. Excessively large cemented carbide powder particle size easily results in uneven distribution, cracks, uneven cobalt phase distribution, and poor gradient transition.

[0020] The cemented carbide powder used in this invention is a Co-WC pre-alloyed powder.

[0021] In a preferred embodiment, the mass ratio of raw material powder to molding agent in the N+M+1 group of filaments is 3~15:1. In the N+M+1 group of filaments of this invention, the raw material powder comprises M parts of cemented carbide powder in different proportions, N parts of mixed powder in different proportions, and one part of pure cBN powder.

[0022] In a preferred embodiment, the molding agent, by mass parts, comprises the following: 30-70 parts of ethylene-vinyl acetate copolymer, 15-25 parts of polycaprolactone, 10-25 parts of thermoplastic polyurethane, 3-10 parts of hydrogenated styrene-butadiene block copolymer, 1-3 parts of tributyl acetylacetonate, 1-2 parts of ethylene bis-stearamide, and 1-2 parts of stearic acid.

[0023] In this invention, the same molding agent is used to prepare different mixed powders. Among the molding agents used, ethylene-vinyl acetate copolymer (EVA) serves as the main binder, providing melt strength and skeletal support; polycaprolactone (PCL) has a low melting point (approximately 60°C) and excellent flowability, significantly reducing the mixing viscosity; thermoplastic polyurethane (TPU) imparts good toughness and bending resistance to the filaments, preventing breakage during the drawing process; hydrogenated styrene-butadiene block copolymer (SEBS) serves as an elastomer toughening agent, further improving the flexibility and dimensional stability of the filaments; tributyl acetylacetonate (ATBC) serves as an environmentally friendly plasticizer, lowering the polymer's glass transition temperature and improving the interfacial wetting between the powder and the binder; ethylene bis-stearamide (EBS) and stearic acid (ABS) serve as internal and external lubricants, reducing mixing torque and screw wear while promoting uniform powder dispersion. The aforementioned multi-component polymers can form a continuous binder phase to encapsulate powder particles during mixing. After extrusion and drawing, the surface is smooth, the roundness is good, and the tensile strength is high, which combines the stiffness and toughness of the filament. In addition, the binders (mainly EVA, TPU, and SEBS) remaining in the solvent degreasing stage of the molding agent used in this invention all contain strong polar groups and have good microwave absorption capabilities, providing a basic condition for microwave-assisted degreasing.

[0024] In a preferred embodiment, the printing is performed using a multi-nozzle FDM 3D printer.

[0025] In the actual printing process, the printing parameters are first set, and the model of each structural layer of the dual-gradient PcBN composite sheet is drawn in the computer. The model is then imported into the slicing software to set the printing parameters, and then imported into the multi-nozzle FDM 3D printer. According to the gradient change requirements of the material composition of each layer, different filaments are switched layer by layer to match the corresponding printing model and print the PcBN composite sheet.

[0026] In a preferred embodiment, the printing speed during the 3D printing process is 10mm / s to 60mm / s, and the printing layer thickness is 0.05 to 0.3mm.

[0027] In a preferred embodiment, the degreasing process involves first solvent degreasing the green body, followed by microwave-assisted degreasing.

[0028] The solvent degreasing process is as follows: the green body is placed in a cyclohexane solution and kept at 40℃~60℃ for 2~4 hours.

[0029] The microwave-assisted degreasing is carried out under a protective atmosphere. The process is as follows: first, a microwave power of 180-400W is used to heat the temperature to 200-250°C at a heating rate of 1-2°C / min, and the temperature is held for 1-2 hours; then, the microwave power is adjusted to 500-800W, and the temperature is heated to 400-450°C at a heating rate of 2-3°C / min, and the temperature is held for 1-3 hours; finally, the microwave power is reduced to 100-300W, and the temperature is increased to 600-650°C at a heating rate of 1-2°C / min, and the temperature is held for 2-4 hours.

[0030] In actual operation, the blanks after solvent degreasing are dried and then placed in a microwave degreasing oven for microwave-assisted degreasing under a nitrogen atmosphere.

[0031] The degreasing process in this invention combines solvent degreasing with microwave-assisted degreasing. First, 10% to 20% of the soluble molding agent is removed using the principle of "like dissolves like" in organic matter, initially forming microscopic exhaust channels. The dried billet is then degreased with microwave heating. After the molding agent reaches its decomposition temperature, it volatilizes and dissipates. Microwave degreasing can directly penetrate the billet, causing the residual polymer molding agent to heat up uniformly throughout, resulting in simultaneous internal and external pyrolysis. The decomposition products diffuse outward through the channels left by the solvent, greatly reducing the risk of fatal defects such as cracking, deformation, or delamination caused by uneven thermal stress. It also significantly reduces the residual carbon content in the degreased billet, ultimately obtaining a degreased billet with pure chemical composition, uniform and interconnected internal pore network, no macroscopic defects, and the ability to maintain self-support. At the same time, the combination of solvent degreasing and microwave-assisted degreasing can significantly shorten the time, reduce energy consumption, and adapt to complex shaped parts.

[0032] However, the microwave degreasing process needs to be effectively controlled. If the power is too high, it will affect the heating rate. If the heating rate is too fast, it will cause the internal gas to be generated explosively, resulting in cracking of the green body or peeling of the surface. If the heating rate is too slow, it will cause the binder to soften, the green body to deform, and prolong the degreasing time. The length of the holding time will affect the final degreasing rate.

[0033] In a preferred embodiment, the high-temperature and high-pressure sintering pressure is 5~8 GPa, the temperature is 1300~1600℃, and the holding time is 5~30 min. After the high-temperature and high-pressure sintering is completed, the pressure is slowly released to obtain a dual-gradient PcBN composite sheet.

[0034] Beneficial effects:

[0035] This invention employs a multi-layered compositional gradient transition layer between the cemented carbide substrate and the PcBN working layer, allowing for a smooth transition in the thermal expansion coefficients of cBN and cemented carbide, effectively alleviating residual thermal stress at the composite material interface. Simultaneously, the use of a cemented carbide substrate with a gradient distribution of cobalt content significantly improves the overall impact toughness of the composite sheet. This dual-gradient structural design effectively enhances interlayer bonding strength, prevents delamination and cracking, and extends the product's service life under complex cutting conditions.

[0036] This invention utilizes FDM 3D printing to prepare PcBN composite preforms with a dual-gradient structure. This allows for precise control of the compositional gradient in the transition layer and the cobalt content in the cemented carbide substrate according to design requirements, achieving accurate optimization of product performance. Simultaneously, 3D printing simplifies the complex processes of traditional powder metallurgy for preparing gradient composite materials, significantly improving production efficiency and reducing manufacturing costs. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of a dual-gradient PcBN composite sheet. Detailed Implementation

[0038] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments.

[0039] Example 1

[0040] The raw materials used are cBN powder and cemented carbide powder. The cBN powder has a particle size of 20 μm, and the cemented carbide powder has a particle size of 10 μm. The cemented carbide powder in the gradient transition layer has a Co content of 15% and a WC content of 85%; the cemented carbide substrate has a Co content of 5-20% and a WC content of 80-95%. The mass ratio of powder to polymer molding agent used for the cBN layer, transition layer, and cemented carbide substrate printing filament is 8:1. The polymer molding agent contains: 60 parts ethylene-vinyl acetate copolymer, 20 parts polycaprolactone, 15 parts thermoplastic polyurethane, 10 parts hydrogenated styrene-butadiene block copolymer, 2 parts tributyl acetylacetonate, 1 part ethylene bis-stearamide, and 1 part stearic acid. The dual-gradient PcBN composite sheet has four gradient transition layers, each with a thickness of 0.05 mm, for a total thickness of 0.2 mm. From the cemented carbide substrate to the CBN layer, the powder content is as follows:

[0041] The first layer contains 80% cemented carbide powder and 20% cBN powder.

[0042] The second layer contains 60% cemented carbide powder and 40% cBN powder.

[0043] The third layer contains 40% cemented carbide powder and 60% cBN powder.

[0044] The fourth layer contains 20% cemented carbide powder and 80% cBN powder.

[0045] In the dual-gradient PcBN composite sheet, the gradient cemented carbide substrate is radially divided into four concentric and coaxial layers. Each layer includes a central concentric cylindrical core and three annular cylindrical layers nested around it from the inside out. The diameter of the concentric cylindrical core is half the diameter of the gradient cemented carbide substrate. The remaining annular cylindrical layers have equal radial thickness. The powder content in each layer of the gradient cemented carbide substrate, from the center outwards, is as follows:

[0046] The first layer contains 80% WC and 20% Co powder.

[0047] The second layer contains 85% WC and 15% Co powder.

[0048] The third layer contains 90% WC and 10% Co powder.

[0049] The fourth layer contains 95% WC and 5% Co powder.

[0050] This example provides a 3D printing process for a dual-gradient structure PcBN composite sheet, including the following steps:

[0051] S1 Preparation of printing filaments: According to the gradient mixing powder and polymer molding agent, the printing filaments required for the corresponding cBN layer, gradient transition layer and gradient cemented carbide substrate are prepared respectively.

[0052] S2 Printing Green Blanks: The filament is sequentially placed into the multi-nozzle FDM printer, and the corresponding printing models are matched sequentially to print the green blanks of each structural layer of the dual-gradient structure PcBN composite sheet. The printing layer thickness is set to 0.05mm and the printing speed is 60mm / s.

[0053] S3 Degreasing: After the green body is assembled, it is placed in a cyclohexane solution and kept at 60°C for 4 hours. Then it is placed in a microwave degreasing furnace for hot degreasing. It is heated to 200°C at a microwave power of 200W and a heating rate of 1°C / min, and held for 1 hour; heated to 400°C at a microwave power of 500W and a heating rate of 2°C / min, and held for 2 hours; heated to 600°C at a microwave power of 100W and a heating rate of 1°C / min, and held for 4 hours. After cooling in the furnace, it is taken out.

[0054] S4 High Temperature and High Pressure Synthesis: The degreased parts are placed into a mold and sintered in a six-sided top press at a temperature of 1500℃ and a pressure of 6GPa for 300s. After sintering, the pressure is slowly released to obtain a dual-gradient PcBN composite sheet.

[0055] After coarse grinding and polishing, the dual-gradient PcBN composite sheet obtained in Example 1 was subjected to wear resistance and thermal stability tests. The wear resistance test used the silicon carbide grinding wheel method, and the relative wear ratio was measured to be ≥520,000, demonstrating excellent wear resistance. Regarding thermal stability, after heating the sample at 700℃ in a protective atmosphere for 20 minutes, no cracks, delamination, or graphitization appeared in the PcBN working layer, and the interface bonding remained intact. The impact toughness tested using the drop hammer impact method reached 12.5 J, significantly better than the average level of commercially available PcBN composite sheet products.

[0056] Example 2

[0057] The raw materials used are cBN powder and cemented carbide powder. The cBN powder has a particle size of 50 μm, and the cemented carbide powder has a particle size of 15 μm. The cemented carbide powder in the gradient transition layer has a Co content of 10% and a WC content of 90%; the cemented carbide substrate has a Co content of 10-20% and a WC content of 80-90%. The mass ratio of powder to polymeric molding agent used for printing filaments in the cBN layer, transition layer, and cemented carbide substrate is 10:1. The polymeric molding agent contains: 45 parts ethylene-vinyl acetate copolymer, 20 parts polycaprolactone, 25 parts thermoplastic polyurethane, 3 parts hydrogenated styrene-butadiene block copolymer, 3 parts tributyl acetylacetonate, 2 parts ethylene bis-stearamide, and 2 parts stearic acid.

[0058] The dual-gradient PcBN composite sheet has 6 gradient transition layers, each with a thickness of 0.05 mm, for a total thickness of 0.3 mm. The powder content from the cemented carbide substrate to the CBN layer is as follows:

[0059] The first layer contains 90% cemented carbide powder and 10% cBN powder.

[0060] The second layer contains 75% cemented carbide powder and 25% cBN powder.

[0061] The third layer contains 60% cemented carbide powder and 40% cBN powder.

[0062] The fourth layer contains 45% cemented carbide powder and 55% cBN powder.

[0063] The fifth layer contains 30% cemented carbide powder and 70% cBN powder.

[0064] The sixth layer contains 15% cemented carbide powder and 85% cBN powder.

[0065] The dual-gradient PcBN composite sheet has a gradient cemented carbide substrate layer consisting of three concentric and coaxial layers radially. Each layer includes a central concentric cylindrical core and three annular cylindrical layers nested around it from the inside out. The diameter of the concentric cylindrical core is one-third of the diameter of the gradient cemented carbide substrate. The remaining annular cylindrical layers have equal radial thickness. The powder content of each layer of the gradient cemented carbide substrate, from the center outwards, is as follows:

[0066] The first layer contains 80% WC and 20% Co powder.

[0067] The second layer contains 85% WC and 15% Co powder.

[0068] The third layer contains 90% WC and 10% Co powder.

[0069] This example provides a 3D printing process for a dual-gradient structure PcBN composite sheet, including the following steps:

[0070] S1 Preparation of printing filaments: According to the gradient mixing powder and polymer molding agent, the printing filaments required for the corresponding cBN layer, gradient transition layer and gradient cemented carbide substrate are prepared respectively.

[0071] S2 Printing Green Blanks: The filament is sequentially placed into the multi-nozzle FDM printer, and the corresponding printing models are matched sequentially to print the green blanks of each structural layer of the dual-gradient structure PcBN composite sheet. The printing layer thickness is set to 0.2mm and the printing speed is 10mm / s.

[0072] S3 Degreasing: After the green body is assembled, it is placed in a cyclohexane solution and kept at 60℃ for 4 hours. Then it is placed in a microwave degreasing furnace for hot degreasing. It is heated to 190℃ with a microwave power of 180W and a heating rate of 1.2℃ / min and held for 1.2 hours. Then it is heated to 410℃ with a microwave power of 550W and a heating rate of 2.2℃ / min and held for 2.2 hours. Finally, it is heated to 610℃ with a microwave power of 120W and a heating rate of 1.2℃ / min and held for 3.5 hours. After cooling in the furnace, it is taken out.

[0073] S4 High Temperature and High Pressure Synthesis: The degreased parts are placed into a mold and sintered in a six-sided top press at a temperature of 1500℃ and a pressure of 6GPa for 300s. After sintering, the pressure is slowly released to obtain a dual-gradient PcBN composite sheet.

[0074] After coarse grinding and polishing, the dual-gradient PcBN composite sheet obtained in Example 2 was subjected to wear resistance and thermal stability tests. The wear resistance test used the silicon carbide grinding wheel method, and the relative wear ratio was measured to be ≥480,000, demonstrating excellent wear resistance. Regarding thermal stability, after heating the sample at 700℃ in a protective atmosphere for 20 minutes, no cracks, delamination, or graphitization appeared in the PcBN working layer, and the interface bonding remained intact. The impact toughness tested using the drop hammer impact method reached 11.8 J, significantly better than the average level of commercially available PcBN composite sheet products.

[0075] Comparative Example 1

[0076] Other conditions remained the same as in Example 1, except that the cemented carbide substrate was adjusted to use a single-component cemented carbide, meaning the Co mass fraction in the entire substrate was 10%. All other printing process parameters were identical to those in Example 1. The product was tested for wear resistance and thermal stability, with a relative wear ratio of approximately 350,000, lower than the 520,000 in Example 1. After heating at 700°C for 20 minutes, slight microcracks appeared at the interface between the PcBN layer and the transition layer, but no delamination occurred. The drop hammer impact toughness was only 6.8 J, significantly lower than the 12.5 J in Example 1. The results indicate that a single substrate without a gradient cannot simultaneously achieve both surface wear resistance and core toughness, resulting in a significant decrease in overall performance.

[0077] Comparative Example 2

[0078] Other conditions remained the same as in Example 2, except for the microwave degreasing process. The green body was directly heated to 600°C using a constant microwave power of 800W and a heating rate of 5°C / min, held for 1 hour, and then cooled in the furnace before being removed. After degreasing, blistering, localized cracking, and even overall collapse were observed on the surface of the green body, making high-temperature, high-pressure synthesis and densification impossible.

[0079] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A dual-gradient PcBN composite sheet, characterized in that: The PcBN composite sheet is divided into a PcBN layer, a gradient transition layer, and a gradient cemented carbide substrate along the axial direction from top to bottom. In the gradient transition layer, the PcBN content gradually decreases and the cemented carbide content gradually increases along the axial direction from top to bottom. In the gradient cemented carbide substrate, the cobalt content changes in a gradient from the center to the radial direction outward.

2. The dual-gradient PcBN composite sheet according to claim 1, characterized in that: The gradient transition layer is divided into N layers along the thickness direction, where N is 2 to 10, and each layer is composed of PcBN and cemented carbide. In the gradient transition layer, the volume fraction of PcBN in the top layer is 75-95%, and the volume fraction of cemented carbide in the top layer is 15-30%. Then, from the second-to-last layer to the bottom layer, based on the content of the top layer, the volume fraction of PcBN decreases by 10-20% layer by layer, and the volume fraction of cemented carbide increases by 10-20% layer by layer. The cemented carbide in the gradient transition layer is Co-WC, with a volume fraction of Co of 5-15% and a volume fraction of WC of 85-95%.

3. The dual-gradient PcBN composite sheet according to claim 1, characterized in that: The cemented carbide in the gradient cemented carbide substrate is Co-WC, wherein the volume fraction of Co is 5-20% and the volume fraction of WC is 80-95%. The gradient cemented carbide substrate is radially divided into M concentric and coaxial layers, where M is 2 to 6. It includes a central concentric cylindrical core and M-1 annular cylindrical layers that are stacked sequentially from the inside to the outside around the concentric cylindrical core. In the concentric cylindrical core, the volume fraction of Co is 15-20% and the volume fraction of WC is 80-85%. Then, from the first annular cylindrical layer to the M-1th annular cylindrical layer, based on the composition of the concentric cylindrical core, the volume fraction of Co decreases by 3-8% layer by layer and the volume fraction of WC increases by 3-8% layer by layer.

4. The dual-gradient PcBN composite sheet according to claim 3, characterized in that: In the gradient cemented carbide substrate, the diameter of the concentric cylindrical core accounts for 1 / 3 to 1 / 2 of the diameter of the gradient cemented carbide substrate, and the remaining annular cylindrical layers are distributed radially with equal thickness.

5. A method for preparing a dual-gradient PcBN composite sheet according to any one of claims 1-4, characterized in that: Based on the composition of the gradient cemented carbide substrate, M parts of cemented carbide powder with different proportions are prepared. Based on the composition of the gradient transition layer, cBN powder and cemented carbide powder are mixed to obtain N parts of mixed powder with different proportions. Then, M parts of cemented carbide powder, N parts of mixed powder and cBN powder are respectively mixed with molding agent, granulated and drawn to obtain N+M+1 groups of filaments. The N+M+1 groups of filaments are printed by a 3D printer to obtain a green blank. The green blank is degreased and sintered under high temperature and high pressure to obtain a dual-gradient PcBN composite sheet.

6. The method for preparing a dual-gradient PcBN composite sheet according to claim 1, characterized in that: The particle size of the cemented carbide powder is ≤30μm, and the particle size of the cBN powder is 10~50μm.

7. The method for preparing a dual-gradient PcBN composite sheet according to claim 1, characterized in that: In the N+M+1 group of filamentous materials, the mass ratio of raw material powder to molding agent is 3~15:1; The molding agent, by mass parts, comprises the following: 30-70 parts of ethylene-vinyl acetate copolymer, 15-25 parts of polycaprolactone, 10-25 parts of thermoplastic polyurethane, 3-10 parts of hydrogenated styrene-butadiene block copolymer, 1-3 parts of tributyl acetylacetonate, 1-2 parts of ethylene bis-stearamide, and 1-2 parts of stearic acid.

8. The method for preparing a dual-gradient PcBN composite sheet according to claim 1, characterized in that: The printing process utilizes a multi-nozzle FDM 3D printer. During the printing process, the printing speed is 10mm / s to 60mm / s, and the printing layer thickness is 0.05 to 0.3mm.

9. The method for preparing a dual-gradient PcBN composite sheet according to claim 1, characterized in that: The degreasing process involves first degreasing the green body with a solvent, and then performing microwave-assisted degreasing. The solvent degreasing process involves placing the green body in a cyclohexane solution and keeping it at 40°C to 60°C for 2 to 4 hours. The microwave-assisted degreasing is carried out under a protective atmosphere. The process is as follows: first, a microwave power of 180-400W is used to heat the temperature to 200-250°C at a heating rate of 1-2°C / min, and the temperature is held for 1-2 hours; then, the microwave power is adjusted to 500-800W, and the temperature is heated to 400-450°C at a heating rate of 2-3°C / min, and the temperature is held for 1-3 hours; finally, the microwave power is reduced to 100-300W, and the temperature is increased to 600-650°C at a heating rate of 1-2°C / min, and the temperature is held for 2-4 hours.

10. The method for preparing a dual-gradient PcBN composite sheet according to claim 1, characterized in that: The high-temperature and high-pressure sintering process involves a pressure of 5-8 GPa, a temperature of 1300-1600℃, and a holding time of 5-30 min.

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