A polycrystalline diamond compact with a continuous gradient transition layer and a 3D printing preparation method thereof

Abstract

The application discloses a polycrystalline diamond compact with a continuous gradient transition layer and a 3D printing preparation method thereof, and the polycrystalline diamond compact is composed of a polycrystalline diamond layer, a continuous gradient transition layer and a hard alloy base from top to bottom, wherein the continuous gradient transition layer is composed of diamond and hard alloy, the content of the hard alloy in the continuous gradient transition layer decreases from 100% to 0, and the content of the diamond increases from 0 to 100% in the direction from the hard alloy base to the polycrystalline diamond layer. The application realizes the continuous change of the diamond and the hard alloy by designing the continuous gradient transition layer and combining the 3D printing technology, so that the material mutation interface in the polycrystalline diamond compact disappears, the internal stress is relieved, and the service performance and the service life of the polycrystalline diamond compact are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of polycrystalline superhard material fabrication, and particularly to a polycrystalline diamond composite sheet with a continuous gradient transition layer and its 3D printing preparation method. Background Technology

[0002] Polycrystalline diamond composites (PDCs) are widely used in cutting tools, oil drill bits, and non-ferrous metal processing due to their combination of the high hardness of diamond and the excellent toughness of cemented carbide. However, due to the significant difference in the coefficients of thermal expansion between diamond and cemented carbide, the PDC layer is prone to peeling off at the interface between the two materials during operation. The key reason is the existence of abrupt changes in physical properties at the interface between the cemented carbide matrix and the PDC layer. This sudden change in material composition often leads to significant local stress concentration, making the interface susceptible to damage. Functionally graded materials (FJTs) can achieve a gradual change in material composition in space. Applying FJTs to the manufacture of PDCs can replace the abrupt interface with a continuous gradient of composition, eliminating the abrupt change in physical properties and minimizing interlayer stress within the PDC, thereby optimizing the structure and overall performance.

[0003] The advantage of using powder-spreading or conventional layer-by-layer 3D printing to fabricate gradient-structured diamond composites is that the composition of the powder material is easy to control. However, because the proportions of each component in the mixed powder must be pre-designed and thoroughly mixed, real-time adjustment is not possible, making it difficult to achieve continuous and uniform changes in the internal composition of the gradient functional material. Therefore, traditional manufacturing technologies with long preparation cycles and complex processes cannot meet the requirements for rapid fabrication of customizable, continuously variable functionally graded materials. A more flexible and efficient manufacturing technology is needed to manufacture polycrystalline diamond composites with continuous gradient transition layers, thereby minimizing the residual stress inside the diamond composite. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, the first objective of this invention is to provide a polycrystalline diamond composite sheet with a continuous gradient transition layer. The polycrystalline diamond composite sheet provided by this invention has a continuous gradient transition layer located between the cemented carbide matrix and the polycrystalline diamond layer, which can reduce the residual stress between the cemented carbide matrix and the polycrystalline diamond layer, increase the bonding strength at the interface between the two materials, and improve the life of the polycrystalline diamond composite sheet.

[0005] The second objective of this invention is to provide a 3D printing method for preparing polycrystalline diamond composite sheets with a continuous gradient transition layer. This process enables the continuous transformation of two materials, diamond and cemented carbide, to complete the fabrication of the continuous gradient transition layer. This not only reduces the manufacturing difficulty of continuous gradient materials but also optimizes the overall performance of the product.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention discloses a polycrystalline diamond composite sheet with a continuous gradient transition layer. The polycrystalline diamond composite sheet is composed of a polycrystalline diamond layer, a continuous gradient transition layer, and a cemented carbide matrix from top to bottom. The continuous gradient transition layer is composed of diamond and cemented carbide. Along the direction from the cemented carbide matrix to the polycrystalline diamond layer, the cemented carbide content in the continuous gradient transition layer decreases from 100% to 0, and the diamond content increases from 0 to 100%.

[0008] This invention provides a polycrystalline diamond composite sheet with a continuous gradient transition layer. The polycrystalline diamond layer contains 100% diamond, and the cemented carbide matrix contains 100% cemented carbide. The continuous gradient transition layer is composed of diamond and cemented carbide. Along the direction from the cemented carbide matrix to the polycrystalline diamond layer, the cemented carbide content decreases from 100% to 0, while the diamond content increases from 0 to 100%. By continuously changing the ratio of diamond to cemented carbide, the abrupt interface between the polycrystalline diamond layer and the cemented carbide matrix disappears, resulting in a heterogeneous material whose properties gradually change with the material composition and structure. This effectively reduces residual stress at the interface between the two materials, improving its performance and lifespan.

[0009] In a preferred embodiment, the cemented carbide is WC-Co, wherein the mass fraction of Co is 3-20% and the mass fraction of WC is 80%-97%.

[0010] In a preferred embodiment, the thickness of the continuous gradient transition layer is 0.1 mm to 3 mm, preferably 0.5 mm to 1 mm. Controlling the thickness of the continuous gradient transition layer within this range yields optimal performance. If the continuous gradient transition layer is too thin, the material transition range is small, failing to effectively reduce the residual stress inside the diamond composite sheet. If it is too thick, the thickness of the cemented carbide matrix and the diamond layer will be correspondingly reduced, decreasing the wear resistance and cutting efficiency of the composite sheet.

[0011] This invention also provides a 3D printing preparation method for polycrystalline diamond composite sheets with a continuous gradient transition layer. Diamond micropowder is sequentially mixed with binder A, granulated, and drawn to obtain diamond polymer composite filaments. WC powder and Co powder are sequentially mixed with binder B, granulated, and drawn to obtain cemented carbide polymer composite filaments. The diamond polymer filaments and cemented carbide polymer filaments are respectively placed into two feed ports of a 3D printer. Based on the model of the polycrystalline diamond composite sheet, the feeding speed of the two filaments is controlled by the feeding system, allowing the two filaments to enter the mixing chamber individually or in different proportions. Then, the filaments are extruded and deposited through a nozzle to obtain a polycrystalline diamond composite sheet green body. The polycrystalline diamond composite sheet green body is then degreased and synthesized under high temperature and high pressure to obtain a gradient structure polycrystalline diamond composite sheet.

[0012] The preparation method of this invention controls the feeding speed of two filaments through the feeding system of a dual-feed single-nozzle FDM printer. When printing a cemented carbide substrate, only the cemented carbide filament is fed in; when printing a polycrystalline diamond layer, only the diamond filament is fed in; and when printing a continuous gradient transition layer, the feeding system controls the different feeding speeds of the two filaments to achieve percentage control of the two materials. After the two filaments melt at high temperature, they flow into the mixing chamber through the drainage chamber under extrusion and are mixed. After the two materials are fully mixed, they are extruded and deposited through a single nozzle to achieve continuous change of diamond and cemented carbide materials, thus completing the manufacturing of a continuous gradient transition layer.

[0013] In a preferred embodiment, the diamond micron powder has a particle size of 1 to 100 μm, the WC powder has a particle size of 100 μm or finer, and the Co powder has a particle size of 100 μm or finer.

[0014] The inventors discovered that controlling the particle size of diamond micron powder and cemented carbide powder within the aforementioned range yields optimal printing accuracy and finished product performance.

[0015] In a preferred embodiment, the mass ratio of the diamond micro powder to the binder A is 2:1 to 20:1.

[0016] In a preferred embodiment, the adhesive A has the following composition by mass percentage: 20-65% ethylene-vinyl acetate copolymer, 5-35% polystyrene, 5-35% styrene-butadiene block copolymer, 3-10% dodecyltrimethylammonium chloride, and 1-5% oleic acid.

[0017] The binder A of this invention uses ethylene-vinyl acetate copolymer as the backbone material. The introduction of short branches formed by polar acetate groups into the ethylene chain alters the original crystalline state, making the ethylene-vinyl acetate copolymer more flexible and elastic, thus imparting better toughness to the filament. The ethylene-vinyl acetate copolymer can withstand high doses of filler and blends well with various organic or inorganic compounds. Furthermore, mixing alloy powder with the ethylene-vinyl acetate copolymer improves the interfacial affinity of the alloy powder and enhances its free formability. Polystyrene possesses advantages such as hardness, high rigidity, good flowability, and a wide processing temperature range, providing high strength for the composite filament. Moreover, this polymer maintains its inherent flowability even under shear and high-temperature conditions in the mixing rotor and extrusion screw. Styrene-butadiene block copolymer is a high-styrene-content impact-resistant polymer. A small amount of butadiene is incorporated into the molecular chain in a multi-block manner, acting as a toughening agent and imparting high impact resistance and elongation at break to the styrene-butadiene block copolymer. Dodecyltrimethylammonium chloride, as a surfactant, can effectively regulate the surface properties and interparticle interactions of diamond particles, forming a monolayer on the surface of the diamond particles. This modifies the powder surface and improves the compatibility of diamond particles with other polymer materials. The anionic surfactant oleic acid adsorbs onto the particle surface, causing it to become electrostatically charged and preventing powder particle agglomeration through electrostatic repulsion. This ensures uniform distribution of the components in the raw material powder within the polymer and improves the molding performance of the mixture. With the synergistic effect of binder component A, the resulting filament exhibits good flexibility, flowability, and uniformity, enabling the printing of green bodies with consistent performance.

[0018] In a preferred embodiment, the diameter of the diamond wire is 1.65–1.85 mm.

[0019] In a preferred embodiment, the mass ratio of the sum of the WC powder and the Co powder to the mass of the binder B is 2:1 to 20:1.

[0020] In a preferred embodiment, the adhesive B, by mass percentage, comprises the following components: 30-75% styrene-butadiene block copolymer, 5-35% polyurethane, 5-10% polyvinyl butyral, 3-6% acrylonitrile-butadiene-styrene copolymer, 3-6% trimellitate, and 1-5% stearic acid.

[0021] The inventors discovered that styrene-butadiene block copolymers possess both the solubility and thermoplasticity of polystyrene and the flexibility and resilience of polybutadiene. They can serve as the main component in hard alloy polymer composites, providing excellent flexibility. Furthermore, styrene-butadiene block copolymers are compatible with many polymers, and the addition of resins and tackifiers can reduce their melt viscosity. Polyurethane is an organic polymer material whose main chain consists of flexible long-chain polyols and rigid isocyanate blocks. It can effectively disperse stress, and the coexistence of polar and non-polar segments improves the chemical stability of polyurethane. Simultaneously, the widespread hydrogen bonding within the polymer further enhances the material's mechanical properties. It can serve as a skeletal material for preparing hard alloy polymer composites, complementing the main component, styrene-butadiene block copolymer. Polyvinyl butyral is a thermoplastic polymer compound. Due to its good cold resistance and adhesion, it exhibits excellent bonding strength to materials such as metals and ceramics, which can better promote the bonding effect between alloy powder and polymer. Acrylonitrile-butadiene-styrene copolymer is a high-strength, tough, and easily processed thermoplastic polymer that enhances the performance of filaments, providing them with strength and ensuring they can smoothly pass through the printer's extrusion gears and be fed into the extrusion nozzle. Tripterygium esters primarily act as plasticizers; plasticizer molecules insert between polymer chains, weakening the intermolecular forces, thereby increasing the mobility of the polymer chains and reducing their crystallinity, thus increasing the polymer's plasticity. Therefore, adding trimellitate esters can improve the plasticity of other polymers. Stearic acid mainly acts as a dispersant, improving the uniformity of cemented carbide powder distribution.

[0022] In a preferred embodiment, the diameter of the cemented carbide wire is 1.65 to 1.85 mm.

[0023] In actual operation, a polycrystalline diamond composite sheet model with a continuous gradient transition layer is created in computer 3D modeling software, and the model file is stored in STL format. Then, the file is directly cut using slicing software to make the thickness of each layer machinable. The final slice file is then imported into the 3D printing equipment. Then, the two types of filaments are placed into the printer's feed port, the equipment is started, and a polycrystalline diamond composite sheet green blank with a continuous gradient transition layer is obtained.

[0024] In a preferred embodiment, based on the model of the polycrystalline diamond composite sheet, the thickness endpoint of the cemented carbide matrix is ​​set as the gradient start point, and the thickness endpoint of the continuous gradient transition layer is set as the gradient end point. Then, the feeding system is first controlled so that only cemented carbide polymer wires enter the mixing chamber. When the gradient start point is reached, the proportion of cemented carbide polymer wires entering the mixing chamber is uniformly reduced according to the thickness of the continuous gradient transition layer, while the proportion of diamond polymer wires entering the mixing chamber is uniformly increased until the gradient end point is reached, at which point only diamond polymer wires enter the mixing chamber.

[0025] In a preferred embodiment, during the deposition printing process, the starting point of the gradient is located at 4–13 mm, the ending point of the gradient is located at 4.1–16 mm, the printing layer thickness is 0.05–0.3 mm, and the printing speed is 10–100 mm / s.

[0026] In a preferred embodiment, the degreasing is performed under vacuum conditions, with a vacuum degree of 2.0 × 10⁻⁶. -2 Pa ~ 8.0 × 10 -4 Pa; The heating program is as follows: first, raise the temperature from room temperature to 80℃~100℃ at a rate of 5~15℃ / min, and hold for 0.5~1h; then raise the temperature to 180℃~230℃ at a rate of 3~10℃ / min, and hold for 1~2.5h; next, raise the temperature to 300℃~330℃ at a rate of 1~5℃ / min, and hold for 0.5~1.5h; then raise the temperature to 400℃~430℃ at a rate of 1~5℃ / min, and hold for 0.5~1.5h; finally, raise the temperature to 550℃~620℃ at a rate of 2~6℃ / min, and hold for 0.5~1h, and then cool with the furnace.

[0027] In the thermal degreasing process of this invention, two different binders are adapted to this invention. At the same time, based on the difference in the pyrolysis temperature range of different components of the binder, a gradient heating mode is adopted for step-by-step degreasing, which can effectively ensure the integrity of the green body and the removal effect of the binder in the green body, and avoid degreasing problems such as bulging, cracking and excessive binder residue.

[0028] In the preferred embodiment, the high-temperature and high-pressure synthesis temperature is 1200℃~1800℃, the synthesis pressure is 4~8GPa, the total synthesis time is 5~25min, and the heat and pressure holding time is 100s~900s.

[0029] In actual operation, the polycrystalline diamond composite preform obtained by printing is placed in a metal cup, and the binder in the preform is removed by solvent degreasing and high temperature degreasing. Then, the metal cup after degreasing is covered with a lid and placed into the synthesis block. The synthesis block is then placed in a six-sided / four-sided / two-sided press for sintering under high temperature and high pressure. After synthesis, the pressure is slowly released and the temperature is lowered to obtain a polycrystalline diamond composite sheet with a continuous gradient transition layer.

[0030] Beneficial effects:

[0031] This invention provides a polycrystalline diamond composite sheet with a continuous gradient transition layer. The continuous gradient transition layer can eliminate the abrupt interface inside the traditional diamond composite sheet, minimize the interlayer stress inside the polycrystalline diamond composite sheet, increase the bonding strength at the interface between the two materials, and achieve the purpose of optimizing the structure and overall performance.

[0032] This invention provides a 3D printing method for preparing polycrystalline diamond composite sheets with a continuous gradient transition layer. This technology can overcome the limitations of traditional processes in manufacturing complex structural tools. By controlling the feeding speed of two filaments through the printer's feeding system, the continuous change of diamond and cemented carbide materials can be achieved to complete the manufacturing of the continuous gradient transition layer. This can significantly improve the production efficiency of continuous gradient materials and reduce production costs. Attached Figure Description

[0033] Figure 1 A schematic diagram of a polycrystalline diamond composite sheet with a continuous gradient transition layer;

[0034] Figure 1 In the middle, 1-polycrystalline diamond layer, 2-continuous gradient transition layer, 3-hard alloy matrix. Detailed Implementation

[0035] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments.

[0036] Example 1

[0037] The design includes a 2mm thick polycrystalline diamond layer, a 1mm thick continuous gradient transition layer, and an 11mm thick cemented carbide substrate. The cemented carbide powder used consists of 10% Co powder and 90% WC powder. The diamond micron powder has a particle size of 30μm, while the WC and Co powders have a particle size of at least 10μm. The mass ratio of diamond micron powder to the special binder A is 3:1. The mass ratio of cemented carbide powder to special binder B is also 3:1. The special binder A comprises 50% ethylene-vinyl acetate copolymer, 25% polystyrene, 15% styrene-butadiene block copolymer, 6% dodecyltrimethylammonium chloride, and 4% oleic acid. The special binder B comprises 55% styrene-butadiene block copolymer, 25% polyurethane, 7% polyvinyl butyral, 5% acrylonitrile-butadiene-styrene copolymer, 4% trimellitate, and 4% stearic acid.

[0038] This example provides a 3D printing process for polycrystalline diamond composite sheets with a continuous gradient transition layer, including the following steps:

[0039] 1) Preparation of printing filament: Diamond micro powder and special binder A are mixed in an internal mixer in a certain proportion to obtain diamond-polymer mixed feed; cemented carbide powder and special binder B are mixed in an internal mixer in a certain proportion to obtain cemented carbide-polymer mixed feed; the two feeds are then fed into a granulator in batches for granulation, and the two granules are then fed into a wire drawing machine for extrusion to obtain diamond-polymer composite filament and cemented carbide-polymer composite filament with diameters of 1.75mm±0.10mm respectively;

[0040] 2) Printing model and parameter design: Draw a model of a polycrystalline diamond composite sheet with a continuous gradient transition layer in the computer, import the model into the slicing software, set the printing parameters, and then export the printing file; The printing parameters are: gradient start position 11mm, gradient end position 12mm, printing layer thickness 0.2mm, and printing speed 50mm / s.

[0041] 3) Green printing: Import the printing file into the printer, then put the two types of filaments into the printer's feed inlet respectively, and start the printer to print a polycrystalline diamond composite green sheet with a continuous gradient transition layer;

[0042] 4) Green body degreasing: The obtained green body is placed in a metal cup, and the special binder in the green body is removed by solvent degreasing and high-temperature degreasing; the special binder is removed by vacuum degreasing process; the green body is placed in a vacuum degreasing furnace for thermal degreasing, with a vacuum degree of 3.0×10 -3 Pa; Degreasing heating procedure: First, increase the temperature from 25℃ to 100℃ at 10℃ / min, and hold at 100℃ for 0.5h; then increase the temperature from 100℃ to 200℃ at 5℃ / min, and hold at 200℃ for 1h; next, increase the temperature from 200℃ to 300℃ at 3℃ / min, and hold at 300℃ for 0.5h; then increase the temperature from 300℃ to 400℃ at 3℃ / min, and hold at 400℃ for 0.5h; finally, increase the temperature from 400℃ to 550℃ at 3℃ / min, and hold at 550℃ for 0.5h. Finally, cool with the furnace and remove the sample.

[0043] 5) Assembly: After degreasing, attach the lid to the metal cup and place it into the synthesis block;

[0044] 6) High temperature and high pressure synthesis: The synthesis block is placed in a six-sided top press and sintered under high temperature and high pressure conditions. The synthesis temperature is 1450℃, the synthesis pressure is 5.5GPa, the total synthesis time is 15min, and the holding time is 200s. After the synthesis is completed, the polycrystalline diamond composite sheet with a continuous gradient transition layer is obtained from the synthesis block.

[0045] After preparing the polycrystalline diamond composite sheet with a continuous gradient transition layer, its performance was tested. The impact resistance of the PDC sample was tested using the falling weight method, and its impact toughness was measured to be 10.8 kJ. Residual stress was detected using laser Raman spectroscopy, and the residual stress at the interface between the polycrystalline diamond layer and the transition layer was measured to be 395 MPa. The failure temperature was tested using a thermal expansion meter, and its thermal expansion failure temperature was measured to be 850 °C. These data demonstrate that the polycrystalline diamond composite sheet with a continuous gradient transition layer prepared using this invention possesses excellent performance.

[0046] Example 2

[0047] The design includes a 2mm thick polycrystalline diamond layer, a 0.5mm thick continuous gradient transition layer, and an 11mm thick cemented carbide substrate. The cemented carbide powder used consists of 10% Co powder and 90% WC powder. The diamond micron powder has a particle size of 30μm, while the WC and Co powders have a particle size of at least 15μm. The mass ratio of diamond micron powder to the special binder A is 3:1. The mass ratio of cemented carbide powder to special binder B is also 3:1. The special binder A comprises 50% ethylene-vinyl acetate copolymer, 25% polystyrene, 15% styrene-butadiene block copolymer, 6% dodecyltrimethylammonium chloride, and 4% oleic acid. The special binder B comprises 55% styrene-butadiene block copolymer, 25% polyurethane, 7% polyvinyl butyral, 5% acrylonitrile-butadiene-styrene copolymer, 4% trimellitate, and 4% stearic acid.

[0048] This example provides a 3D printing process for polycrystalline diamond composite sheets with a continuous gradient transition layer, including the following steps:

[0049] 1) Preparation of printing filament: Diamond micro powder and special binder A are mixed in an internal mixer in a certain proportion to obtain diamond polymer composite feed; cemented carbide powder and special binder B are mixed in an internal mixer in a certain proportion to obtain cemented carbide polymer composite feed; the two feeds are then fed into a granulator in batches for granulation, and the two granules are then fed into a wire drawing machine for extrusion to obtain diamond polymer composite filament and cemented carbide polymer composite filament with diameters of 1.75mm±0.10mm respectively;

[0050] 2) Printing model and parameter design: Draw a model of a polycrystalline diamond composite sheet with a continuous gradient transition layer in the computer, import the model into the slicing software, set the printing parameters, and then export the printing file; the printing parameters are: gradient start position 11mm, gradient end position 13mm, printing layer thickness 0.2mm, and printing speed 50mm / s.

[0051] 3) Green printing: Import the printing file into the printer, then put the two types of filaments into the printer's feed inlet respectively, and start the printer to print a polycrystalline diamond composite green sheet with a continuous gradient transition layer;

[0052] 4) Green body degreasing: The obtained green body is placed in a metal cup, and the special binder in the green body is removed by solvent degreasing and high-temperature degreasing; the special binder is removed by vacuum degreasing process; the green body is placed in a vacuum degreasing furnace for thermal degreasing, with a vacuum degree of 3.0×10 -3 Pa; Degreasing heating procedure: First, increase the temperature from 25℃ to 100℃ at 10℃ / min, and hold at 100℃ for 0.5h; then increase the temperature from 100℃ to 200℃ at 5℃ / min, and hold at 200℃ for 1h; next, increase the temperature from 200℃ to 300℃ at 3℃ / min, and hold at 300℃ for 0.5h; then increase the temperature from 300℃ to 400℃ at 3℃ / min, and hold at 400℃ for 0.5h; finally, increase the temperature from 400℃ to 550℃ at 3℃ / min, and hold at 550℃ for 0.5h. Finally, cool with the furnace and remove the sample.

[0053] 5) Assembly: After degreasing, attach the lid to the metal cup and place it into the synthesis block;

[0054] 6) High temperature and high pressure synthesis: The synthesis block is placed in a six-sided top press and sintered under high temperature and high pressure conditions. The synthesis temperature is 1450℃, the synthesis pressure is 5.5GPa, the total synthesis time is 15min, and the holding time is 200s. After the synthesis is completed, the polycrystalline diamond composite sheet with a continuous gradient transition layer is obtained from the synthesis block.

[0055] After preparing the polycrystalline diamond composite sheet with a continuous gradient transition layer, its performance was tested. The impact resistance of the PDC sample was tested using the falling weight method, and its impact toughness was measured to be 11.8 kJ. Residual stress was detected using laser Raman spectroscopy, and the residual stress at the interface between the polycrystalline diamond layer and the transition layer was measured to be 215 MPa. The failure temperature was tested using a thermal expansion meter, and its thermal expansion failure temperature was measured to be 865 °C. These data demonstrate that the polycrystalline diamond composite sheet with a continuous gradient transition layer prepared using this invention possesses excellent performance.

[0056] Example 3

[0057] The design includes a 2mm thick polycrystalline diamond layer, a 1mm thick continuous gradient transition layer, and an 11mm thick cemented carbide substrate. The cemented carbide powder used consists of 10% Co powder and 90% WC powder. The diamond micron powder has a particle size of 30μm, while the WC and Co powders have a particle size of at least 20μm. The mass ratio of diamond micron powder to the special binder A is 4:1. The mass ratio of cemented carbide powder to special binder B is also 4:1. The special binder A comprises 50% ethylene-vinyl acetate copolymer, 25% polystyrene, 15% styrene-butadiene block copolymer, 6% dodecyltrimethylammonium chloride, and 4% oleic acid. The special binder B comprises 55% styrene-butadiene block copolymer, 25% polyurethane, 7% polyvinyl butyral, 5% acrylonitrile-butadiene-styrene copolymer, 4% trimellitate, and 4% stearic acid.

[0058] This example provides a 3D printing process for polycrystalline diamond composite sheets with a continuous gradient transition layer, including the following steps:

[0059] 1) Preparation of printing filament: Diamond micro powder and special binder A are mixed in an internal mixer in a certain proportion to obtain diamond polymer composite feed; cemented carbide powder and special binder B are mixed in an internal mixer in a certain proportion to obtain cemented carbide polymer composite feed; the two feeds are then fed into a granulator in batches for granulation, and the two granules are then fed into a wire drawing machine for extrusion to obtain diamond polymer composite filament and cemented carbide polymer composite filament with diameters of 1.75mm±0.10mm respectively;

[0060] 2) Printing model and parameter design: Draw a model of a polycrystalline diamond composite sheet with a continuous gradient transition layer in the computer, import the model into the slicing software, set the printing parameters, and then export the printing file; the printing parameters are: gradient start position 11mm, gradient end position 13mm, printing layer thickness 0.2mm, and printing speed 50mm / s.

[0061] 3) Green printing: Import the printing file into the printer, then put the two types of filaments into the printer's feed inlet respectively, and start the printer to print a polycrystalline diamond composite green sheet with a continuous gradient transition layer;

[0062] 4) Green body degreasing: The obtained green body is placed in a metal cup, and the special binder in the green body is removed by solvent degreasing and high-temperature degreasing; the special binder is removed by vacuum degreasing process; the green body is placed in a vacuum degreasing furnace for thermal degreasing, with a vacuum degree of 3.0×10 -3Pa; Degreasing heating procedure: First, increase the temperature from 25℃ to 100℃ at 10℃ / min, and hold at 100℃ for 0.5h; then increase the temperature from 100℃ to 200℃ at 5℃ / min, and hold at 200℃ for 1h; next, increase the temperature from 200℃ to 300℃ at 3℃ / min, and hold at 300℃ for 0.5h; then increase the temperature from 300℃ to 400℃ at 3℃ / min, and hold at 400℃ for 0.5h; finally, increase the temperature from 400℃ to 550℃ at 3℃ / min, and hold at 550℃ for 0.5h. Finally, cool with the furnace and remove the sample.

[0063] 5) Assembly: After degreasing, attach the lid to the metal cup and place it into the synthesis block;

[0064] 6) High temperature and high pressure synthesis: The synthesis block is placed in a six-sided top press and sintered under high temperature and high pressure conditions. The synthesis temperature is 1550℃, the synthesis pressure is 6GPa, the total synthesis time is 18min, and the holding time is 200s. After the synthesis is completed, the polycrystalline diamond composite sheet with a continuous gradient transition layer is obtained from the synthesis block.

[0065] After preparing the polycrystalline diamond composite sheet with a continuous gradient transition layer, its performance was tested. The impact resistance of the PDC sample was tested using the falling weight method, and its impact toughness was measured to be 12.1 kJ. Residual stress was detected using laser Raman spectroscopy, and the residual stress at the interface between the polycrystalline diamond layer and the transition layer was measured to be 185 MPa. The failure temperature was tested using a thermal expansion meter, and its thermal expansion failure temperature was measured to be 872 °C. These data demonstrate that the polycrystalline diamond composite sheet with a continuous gradient transition layer prepared using this invention possesses excellent performance.

[0066] Comparative Example 1

[0067] All other conditions were the same as in Example 1, with the continuous gradient transition layer designed to be 0.05 mm thick. Because the continuous gradient transition layer was too thin, the material transition range was small, failing to effectively reduce the residual stress inside the diamond composite sheet; the residual stress value reached 795 MPa.

[0068] Comparative Example 2

[0069] All other conditions were the same as in Example 2, but the vacuum degree during the degreasing process was -0.08 MPa, and the degreased blanks were obviously oxidized, which directly affected the synthesis effect of the diamond composite sheet. The synthesized polycrystalline diamond composite sheet had pits and edge chipping problems.

[0070] Comparative Example 3

[0071] All other conditions were the same as in Example 3, but the synthesis pressure and temperature were set to 3.5 GPa. Due to the low sintering pressure, the polycrystalline diamond layer was not completely sintered. After the sample was taken out and sandblasted, the polycrystalline diamond layer fell off directly, and a qualified polycrystalline diamond composite sheet could not be obtained.

[0072] 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 method for preparing a polycrystalline diamond composite sheet with a continuous gradient transition layer, characterized in that: Diamond micro powder and binder A are sequentially mixed, granulated, and drawn to obtain diamond polymer composite filaments. WC powder and Co powder are sequentially mixed, granulated, and drawn to obtain cemented carbide polymer composite filaments. The diamond polymer composite filaments and cemented carbide polymer composite filaments are placed into two feed ports of a 3D printer, respectively. Based on the model of the polycrystalline diamond composite sheet, the thickness endpoint of the cemented carbide matrix is ​​set as the gradient start point, and the thickness endpoint of the continuous gradient transition layer is set as the gradient endpoint. Then, the feeding system is first controlled so that only cemented carbide polymer filaments enter the mixing chamber. When the gradient start point is reached, the proportion of cemented carbide polymer filaments entering the mixing chamber is uniformly decreased, and the proportion of diamond polymer filaments entering the mixing chamber is uniformly increased, according to the thickness of the continuous gradient transition layer, until the gradient endpoint is reached, where only diamond polymer filaments enter the mixing chamber. Then, the polycrystalline diamond composite sheet is obtained by extrusion deposition printing through a nozzle. The polycrystalline diamond composite sheet preform is then degreased and synthesized under high temperature and high pressure to obtain a gradient structure polycrystalline diamond composite sheet. The adhesive A, by mass percentage, comprises the following components: 20-65% ethylene-vinyl acetate copolymer, 5-35% polystyrene, 5-35% styrene-butadiene block copolymer, 3-10% dodecyltrimethylammonium chloride, and 1-5% oleic acid. The adhesive B, by mass percentage, comprises the following components: 30-75% styrene-butadiene block copolymer, 5-35% polyurethane, 5-10% polyvinyl butyral, 3-6% acrylonitrile-butadiene-styrene copolymer, 3-6% trimellitate, and 1-5% stearic acid. During the deposition printing process, the gradient start point is located at 4~13mm, the gradient end point is located at 4.1~16mm, the printing layer thickness is 0.05~0.3mm, and the printing speed is 10~100mm / s. The polycrystalline diamond composite sheet is composed of a polycrystalline diamond layer, a continuous gradient transition layer, and a cemented carbide matrix from top to bottom. The continuous gradient transition layer is composed of diamond and cemented carbide. Along the direction from the cemented carbide matrix to the polycrystalline diamond layer, the cemented carbide content in the continuous gradient transition layer decreases from 100% to 0, and the diamond content increases from 0 to 100%.

2. The method for preparing a polycrystalline diamond composite sheet with a continuous gradient transition layer according to claim 1, characterized in that: The mass ratio of the diamond micro powder to binder A is 2:1 to 20:1; The diameter of the diamond polymer composite wire is 1.65 to 1.85 mm.

3. The method for preparing a polycrystalline diamond composite sheet with a continuous gradient transition layer according to claim 1, characterized in that: The mass ratio of the sum of the WC powder and the Co powder to the mass of the binder B is 2:1 to 20:1; The diameter of the hard alloy polymer composite wire is 1.65 to 1.85 mm.

4. The method for preparing a polycrystalline diamond composite sheet with a continuous gradient transition layer according to claim 1, characterized in that: The degreasing is performed under vacuum conditions, with a vacuum degree of 2.0 × 10⁻⁶. -2 Pa ~ 8.0 × 10 -4 Pa; The heating program is as follows: first, raise the temperature from room temperature to 80℃~100℃ at a rate of 5~15℃ / min, and hold for 0.5~1h; then raise the temperature to 180℃~230℃ at a rate of 3~10℃ / min, and hold for 1~2.5h; next, raise the temperature to 300℃~330℃ at a rate of 1~5℃ / min, and hold for 0.5~1.5h; then raise the temperature to 400℃~430℃ at a rate of 1~5℃ / min, and hold for 0.5~1.5h; finally, raise the temperature to 550℃~620℃ at a rate of 2~6℃ / min, and hold for 0.5~1h, and then cool with the furnace.

5. The method for preparing a polycrystalline diamond composite sheet with a continuous gradient transition layer according to claim 1, characterized in that: The high-temperature and high-pressure synthesis temperature is 1200℃~1800℃, the synthesis pressure is 4~8GPa, the total synthesis time is 5~25min, and the heat and pressure holding time is 100s~900s.

6. A polycrystalline diamond composite sheet with a continuous gradient transition layer according to claim 1, characterized in that: The cemented carbide is WC-Co, wherein the mass fraction of Co is 3-20% and the mass fraction of WC is 80%-97%.

7. A polycrystalline diamond composite sheet with a continuous gradient transition layer according to claim 1, characterized in that: The thickness of the continuous gradient transition layer is 0.1 mm to 3 mm.

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