A polycrystalline diamond composite sheet with a ripple-shaped gradient layer and a preparation method thereof

Abstract

The present invention relates to a polycrystalline diamond composite sheet with a rippled wavy gradient layer and a preparation method thereof. The polycrystalline diamond composite sheet is composed of a cemented carbide substrate, a multi-layer rippled wavy gradient layer and a polycrystalline diamond layer from bottom to top. In the rippled wavy gradient layer, the content of polycrystalline diamond increases from bottom to top, and the content of cemented carbide decreases from bottom to top. In the rippled wavy gradient layer, the amplitude of the rippled wavy structure is 0.2-0.6 mm, the wavelength is 1-2 mm, and the upper and lower ripple spacing in the top layer is set to a gradual change of (t / 2-t) mm-t mm from the crest to the trough. The upper and lower ripple spacings of the remaining layers are all t mm, where t is 0.05-0.4. The present invention changes the upper and lower two-layer structure of the traditional polycrystalline diamond composite sheet into a multi-layer structure with a rippled wavy gradient layer, solving the problems of low interface bonding strength and large internal residual stress of the polycrystalline diamond composite sheet.

Description

Technical Field

[0001] The invention belongs to the technical field of polycrystalline diamond composite sheet preparation, and in particular relates to a polycrystalline diamond composite sheet with a ripple wave gradient layer and a preparation method thereof. Background Art

[0002] Polycrystalline diamond composite sheets are made by sintering a diamond layer and a cemented carbide substrate under ultra-high pressure and high temperature conditions. They have the high hardness and high wear resistance of diamond and the high strength and impact toughness of cemented carbide, and are widely used in oil drilling, geological drilling, engineering drilling, mechanical processing and other fields. Due to the large difference in the thermal expansion coefficients of diamond and cemented carbide, there is severe residual stress at the interface between the polycrystalline diamond layer (PCD layer) and the cemented carbide substrate, which causes the failure of the polycrystalline diamond composite sheet such as delamination between the polycrystalline diamond layer and the cemented carbide substrate.

[0003] There are currently two ways to enhance the interface bonding strength between the PCD layer and the cemented carbide substrate. The first is non-planar connection technology, which improves the interface bonding strength and structural shear resistance by designing irregular interface structures, such as grooves and serrated shapes. The second is to add a gradient transition layer, which uses the gradient transition method to ease the difference in thermal expansion coefficients between the two materials to reduce the huge residual stress.

[0004] Both of the above methods have their own defects and shortcomings. Although changing the interface structure can improve the impact resistance and interface bonding performance, the common irregular interface structure generally has local stress concentration problems, and it is impossible to effectively reduce the residual stress at the interface. Similarly, the residual stress can be effectively reduced by setting a gradient transition layer, but the conventional gradient transition layer is usually a planar connection type and has a small number of layers. Not only can it not effectively improve the bonding strength of the interface, but the reduction of residual stress is limited. Therefore, combining the two methods can greatly reduce the failure risk of the composite sheet. However, the current traditional process for preparing PDC composite sheets is difficult to prepare polycrystalline diamond composite sheets with complex structures and a large number of gradient transition layers. Summary of the invention

[0005] In view of the problems and shortcomings of the above-mentioned prior art, the first object of the present invention is to provide a polycrystalline diamond composite sheet with a rippled wavy gradient layer. By providing a rippled wavy gradient layer, the interface bonding strength is improved, the residual stress inside the composite sheet is reduced, and the problem of delamination between the polycrystalline diamond layer and the cemented carbide substrate during actual use is solved.

[0006] The second object of the present invention is to provide a method for preparing a polycrystalline diamond compact having a rippled wavy gradient layer. The preparation of the polycrystalline diamond compact having a rippled wavy gradient layer is achieved by using fused deposition modeling (FDM) 3D printing technology.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] The present invention provides a polycrystalline diamond composite sheet with a rippled wavy gradient layer: the polycrystalline diamond composite sheet is composed of a cemented carbide substrate, a multi-layered rippled wavy gradient layer and a polycrystalline diamond layer from bottom to top; in the rippled wavy gradient layer, the content of polycrystalline diamond increases from bottom to top, and the content of cemented carbide decreases from bottom to top; in the rippled wavy gradient layer, the amplitude of the rippled wavy structure is 0.2-0.6 mm, the wavelength is 1-2 mm, the upper and lower ripple spacing in the top layer is set to a gradient of (t / 2-t) mm-t mm from the crest to the trough, and the upper and lower ripple spacings of the remaining layers are all t mm, wherein t is 0.05-0.4.

[0009] The polycrystalline diamond composite sheet provided by the present invention is provided with a rippled wavy gradient layer with a multi-layer corrugated cross-section in the middle. The interface bonding area is increased by adopting a rippled wavy interface structure. This interface structure also makes the stress distribution of the polycrystalline diamond composite sheet non-directional, disperses the interface stress and improves the impact resistance. At the same time, the upper and lower ripple spacing of the topmost gradient layer combined with the polycrystalline diamond layer gradually changes from the crest to the trough, improving the local stress concentration phenomenon common in traditional irregular interface structures. In addition, the setting of the multi-layer gradient layer can effectively alleviate the huge residual stress caused by the difference in thermal expansion coefficient between the polycrystalline diamond layer and the cemented carbide substrate, and reduce the quality risk of delamination of the polycrystalline diamond layer and the cemented carbide substrate during actual use.

[0010] The inventors found that in order to optimize the performance of the final polycrystalline diamond composite sheet, it is necessary to effectively control the spacing between the upper and lower corrugations. If the spacing between the upper and lower corrugations of any layer is too large, it will cause excessive stress changes between the layers, resulting in a decrease in the strength of the composite sheet. If it is too small, the irregular features will not be obvious and will be similar to the traditional planar structure, with the defect of easy interface cracking.

[0011] In a preferred solution, the cemented carbide in the cemented carbide substrate and the rippled wave gradient layer is Co-WC, wherein the mass fraction of Co is 5-25%, and the mass fraction of WC is 75-95%.

[0012] In a preferred solution, the ripple-shaped gradient layer is divided into n layers, and n is 3 to 16 layers. The inventors found that controlling the number of layers within the above range results in the best performance of the final product, while too many layers will increase the cost and the advantages will not be obvious, and too few layers will fail to take advantage of the gradient transition.

[0013] In a preferred embodiment, in the rippled wavy gradient layer, the volume fraction of polycrystalline diamond in the bottom layer is 5-15%, and then the volume fraction increases by 5-30% per layer from the second bottom layer to the top layer; the volume fraction of polycrystalline diamond in the top layer is 85-95%, and the volume fraction of cemented carbide in the bottom layer is 85-95%, and then the volume fraction decreases by 5-30% per layer from the second bottom layer to the top layer.

[0014] The inventors found that in the ripple-shaped gradient layer, the performance of the polycrystalline diamond composite sheet obtained by gradual change in the above manner is optimal. However, if the volume fraction gradient is unreasonable, the gradient transition of the material cannot be achieved. A sudden increase or decrease in the composition in a certain layer will increase the residual stress.

[0015] In a preferred embodiment, the top surface of the cemented carbide substrate and the bottom surface of the polycrystalline diamond layer are both ripple-shaped.

[0016] The present invention also provides a method for preparing a polycrystalline diamond composite sheet with a ripple wavy gradient layer, comprising mixing and granulating diamond powder and a binder to obtain polycrystalline diamond layer granules, respectively preparing diamond powder, WC-Co alloy powder and a binder according to the design components of each layer in the ripple wavy gradient layer, mixing and granulating to obtain N groups of ripple wavy gradient layer granules, and then 3D printing the polycrystalline diamond layer granules to obtain a polycrystalline diamond layer green body, using PVA (polyvinyl alcohol) as a support layer material, alternately printing PVA (polyvinyl alcohol) and N groups of ripple wavy gradient layer granules layer by layer to obtain a ripple wavy gradient layer green body A with a support structure, removing the support structure from the ripple wavy gradient layer green body with a support structure to obtain a ripple wavy gradient layer green body B, assembling the ripple wavy gradient layer green body B and the polycrystalline diamond layer green body into one to obtain a composite green body, degreasing the composite green body to obtain a degreased composite green body, assembling the degreased composite green body with a cemented carbide substrate, and synthesizing at high temperature and high pressure to obtain a polycrystalline diamond composite sheet.

[0017] In a preferred embodiment, the particle size of the diamond powder is 0.5 to 100 μm, and the particle size of the WC-Co alloy powder is 0.5 to 150 μm.

[0018] According to a preferred embodiment, the binders in the polycrystalline diamond layer granules and the N groups of rippled wavy gradient layer granules are composed, by mass percentage, of 8-35% paraffin wax (PW), 20-26% polymethyl methacrylate (PMMA), 20-26% ethylene-vinyl acetate copolymer (EVA), 18-24% polyethylene (LDPE), 3-8% epoxidized soybean oil (ESO), and 1-3% stearic acid.

[0019] The binder of the present invention uses paraffin wax (PW) and epoxidized soybean oil (ESO) as filling phases to adjust wettability, adds stearic acid as a surfactant, adds polymethyl methacrylate (PMMA), low-density polyethylene (LDPE), and ethylene-vinyl acetate copolymer (EVA) to adjust the strength and viscosity of the binder, and confirms the range of each component through a large number of experiments. By using the above-mentioned binder components, the molding granules in the present invention can ensure the uniformity of the distribution of cemented carbide and diamond powder, reduce agglomeration, and ensure the quality of molding. The inventor found that the content of each component of the binder should be controlled within a given range, otherwise it will affect the printing performance of the granular material.

[0020] In a preferred embodiment, in the polycrystalline diamond layer granules, the mass ratio of binder to diamond powder is 1:2-20.

[0021] According to a preferred solution, in the N groups of rippled wavy gradient layer particles, the mass ratio of binder: (diamond powder+WC-Co alloy powder) is 1:2-20.

[0022] In a preferred embodiment, diamond powder and a binder are kneaded at 150° C. to 350° C. for 60 to 120 minutes and granulated to obtain polycrystalline diamond layer granules.

[0023] The inventors found that it is crucial to first prepare polycrystalline diamond layer granules and then use fused deposition printing to form them. If silk materials are made, since the binder content in the silk materials is higher than that in the granules, the ripple wave structure of the product will be destroyed during the degreasing process of the molded green body due to the high binder content, and slurry direct writing cannot form them.

[0024] The preferred solution is to prepare diamond powder, WC-Co alloy powder and binder according to the designed components of each layer in the ripple wavy gradient layer, mix them at 150℃~350℃ for 60~120min, and granulate them to obtain N groups of ripple wavy gradient layer granules.

[0025] In the actual operation process of the present invention, mixing is carried out in an internal mixer, and the internal mixer feed is obtained and sent to a granulator for granulation. After obtaining polycrystalline diamond layer granules and N groups of ripple wavy gradient layer granules by granulation, the models of the ripple wavy gradient layer, the support layer for supporting the ripple wavy gradient layer, and the polycrystalline diamond layer are respectively established in the computer, and the models are imported into the slicing software for assembly and slicing settings, and printing parameter settings. After the settings are completed, the files are imported into the granular FDM printer; then PVA (polyvinyl alcohol) is used as the support layer material, and PVA (polyvinyl alcohol), N groups of ripple wavy gradient layer granules, and polycrystalline diamond layer granules are respectively placed in the feeding system of the double-extrusion double-nozzle granular FDM printer, and PVA (polyvinyl alcohol) and N groups of ripple wavy gradient layer granules are alternately printed layer by layer to obtain a ripple wavy gradient layer green body A with a support structure, and the polycrystalline diamond layer granules are printed to obtain a polycrystalline diamond layer green body.

[0026] In a preferred embodiment, in the process of obtaining a polycrystalline diamond layer green body by 3D printing of polycrystalline diamond layer granules, the nozzle diameter used is 0.2-4 mm, the layer height is 0.05-2 mm, the extrusion rate is 2-200 mm / s, and the extrusion flow rate is 100-180%.

[0027] A preferred solution is that in the process of alternately printing PVA (polyvinyl alcohol) and N groups of rippled wavy gradient layer granules layer by layer to obtain a rippled wavy gradient layer green body A with a support structure, when printing PVA, the nozzle diameter used is 0.4-0.8mm, the layer height is 0.2-0.4mm, the extrusion rate is 100-200mm / s, and the extrusion flow rate is 120-180%; when printing N groups of rippled wavy gradient layer granules, the nozzle diameter used is 0.2-4mm, the layer height is 0.05-2mm, the extrusion rate is 2-200mm / s, and the extrusion flow rate is 100-180%.

[0028] In a preferred embodiment, the corrugated wavy gradient layer green body with a support structure is placed in a water bath at 75-90° C. to remove the support structure to obtain the corrugated wavy gradient layer green body B.

[0029] In a preferred embodiment, the degreasing is carried out in a hydrogen atmosphere, the hydrogen flow rate during degreasing is 3-5 L / min, and the heating program during degreasing is: first, the temperature is increased from room temperature to 100-150°C at a heating rate of 5-10°C / min, and kept warm for 75-100 min; then, the temperature is increased to 350-400°C at a heating rate of 2-6°C / min, and kept warm for 45-60 min; then, the temperature is increased to 500-550°C at a heating rate of 1-5°C / min, and kept warm for 90-120 min.

[0030] In the thermal debinding process of the present invention, based on the differences in the pyrolysis temperature ranges of different components of the binder, a gradient heating mode is used for step-by-step debinding, which can effectively ensure the integrity of the green body and the removal of the binder in the green body, and avoid debinding defects.

[0031] In a preferred embodiment, the pressure of the high temperature and high pressure synthesis is 2 to 8.5 GPa, the temperature of the high temperature and high pressure synthesis is 1200 to 1850° C., and the time of the high temperature and high pressure synthesis is 300 to 1000 s.

[0032] Beneficial Effects

[0033] The present invention provides a polycrystalline diamond composite sheet with a rippled wavy gradient structure. The polycrystalline diamond composite sheet increases the interface bonding area by adopting a rippled wavy interface structure. This interface structure also makes the stress distribution of the polycrystalline diamond composite sheet non-directional, disperses the interface stress and improves the impact resistance. At the same time, the upper and lower ripple spacing of the topmost gradient layer combined with the polycrystalline diamond layer gradually changes from the crest to the trough, improving the local stress concentration phenomenon common in traditional irregular interface structures. In addition, the setting of multiple gradient layers can effectively alleviate the huge residual stress caused by the difference in thermal expansion coefficients between the polycrystalline diamond layer and the cemented carbide substrate, reducing the quality risk of delamination of the polycrystalline diamond layer and the cemented carbide substrate during actual use.

[0034] The present invention adopts FDM fused deposition modeling 3D printing technology, breaking the limitations of traditional processes in preparing polycrystalline diamond composite sheets with complex interfaces and multi-layer gradient layer structures, and realizing the preparation of polycrystalline diamond composite sheets with ripple-shaped gradient layers. Multiple particle FDM printers are used to print green sheets with different structural layers respectively. After the quality of different green sheets is inspected and qualified, they are assembled and degreased and sintered to achieve assembly line production and precise quality control, greatly improving the production efficiency and product qualification rate of polycrystalline diamond composite sheets. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagram of a polycrystalline diamond composite sheet with a rippled wavy gradient layer.

[0036] Figure 2 Schematic diagram of the cross-sectional structure of a polycrystalline diamond composite sheet with a ripple-shaped gradient layer along the diameter.

[0037] in, Figure 1 and Figure 2 Middle: 1-polycrystalline diamond layer; 2-rippled wavy gradient layer; 3-cemented carbide substrate; 4-uppermost gradient layer. DETAILED DESCRIPTION

[0038] Embodiment 1:

[0039] The polycrystalline diamond composite sheet with a ripple wavy gradient layer includes three parts: a polycrystalline diamond layer, a ripple wavy gradient layer, and a cemented carbide substrate. The diameter × height size of the polycrystalline diamond composite sheet of design model 1613 is 16.00mm × 13.20mm. The amplitude of the ripple wavy structure is 0.4mm and the wavelength is 1mm. The height of the cemented carbide substrate and the gradient layer from the crest to the trough is 0.4mm, of which the crest is 0.2mm high, and the height of the cemented carbide substrate from the crest to the bottom surface is 11.2mm. The upper and lower ripple spacing of the uppermost layer of the gradient layer is a gradual change of 0.1mm to 0.2mm from the crest to the trough, and the upper and lower ripple spacing of each layer except the uppermost layer is 0.2mm. The height of the polycrystalline diamond layer and the gradient layer from the crest to the trough is 0.3mm, of which the crest is 0.1mm high, and the height of the polycrystalline diamond layer from the crest to the top surface is 0.9mm.

[0040] The cemented carbide substrate is made of YG15 (WC-15wt%Co) alloy, in which the mass fractions of WC and Co are WC85% and Co15%. Six ripple wave gradient layers are set, and the volume content of diamond in each layer from bottom to top is 10%, 25%, 40%, 55%, 70%, and 85%, respectively, and the volume content of YG15 in each corresponding gradient layer is 90%, 75%, 60%, 45%, 30%, and 15%, respectively. The particle size of YG15 pre-alloyed powder is 25-30μm, and the particle size of diamond powder is 15-20μm.

[0041] The production process is as follows:

[0042] Step 1: Take an appropriate amount of diamond powder and YG15 pre-alloyed powder; mix them according to the set proportions of the polycrystalline diamond layer and each gradient layer, place the mixed powder in an internal mixer at 260°C for internal mixing, add a certain proportion of special binder, the mass ratio of the special binder to the powder is 1:15, wherein the mass fractions of PW, PMMA, EVA, LDPE, ESO, and stearic acid are 30%, 23%, 22%, 20%, 4%, and 1%, respectively, and internal mixing for 110 minutes, then send the internal mixing feed into a granulator for granulation to obtain a molding material;

[0043] Step 2: Model the 6 gradient layers, the polycrystalline diamond layer and the supporting structure of the gradient layer in the computer, assemble and slice the model files using slicing software, and import the final 7 slice files into the granular FDM printer respectively;

[0044] Step 3: Put the molding material and the water-soluble support material PVA (polyvinyl alcohol) into the two feed hoppers of the dual-extrusion dual-nozzle granular FDM printer respectively, and obtain the gradient layer green body and polycrystalline diamond layer green body with support structure after printing. Set the particle printing parameters: the nozzle diameter used for molding material printing is 0.4mm, the layer height is 0.1mm, the extrusion rate is 35mm / s, and the extrusion flow rate is 120%; the nozzle diameter used for PVA printing is 0.8mm, the layer height is 0.4mm, the extrusion rate is 120mm / s, and the extrusion flow rate is 130%;

[0045] Step 4: placing the gradient layer green body containing the support structure in a beaker filled with water and heating it in a water bath at 80°C to dissolve the support, and after the support is completely dissolved, obtaining the gradient layer green body with the support removed;

[0046] Step 5: Place the printed green sheets in a metal cup in order and put them into a debinding furnace for debinding. The debinding process parameters are: in the first stage, the temperature is increased to 150°C at a heating rate of 5°C / min and kept warm for 75 minutes; in the second stage, the temperature is increased to 400°C at a heating rate of 4°C / min and kept warm for 50 minutes; in the third stage, the temperature is increased to 550°C at a heating rate of 2°C / min and kept warm for 100 minutes. The atmosphere is hydrogen and the hydrogen flow rate is 5L / min.

[0047] Step 6: Place the degreased sample and cemented carbide substrate into a six-sided hydraulic press, increase the pressure to 5.5 GPa, increase the temperature to 1500°C, and maintain the pressure and temperature for 600 seconds. Then stop heating, reduce the pressure, and allow the equipment temperature to reach room temperature. After the pressure drops to standard atmospheric pressure, take out the polycrystalline diamond composite sheet with a ripple-shaped gradient layer from the six-sided hydraulic press.

[0048] Embodiment 2:

[0049] The polycrystalline diamond composite sheet with a ripple wavy gradient layer includes three parts: a polycrystalline diamond layer, a ripple wavy gradient layer, and a cemented carbide substrate. The diameter × height size of the polycrystalline diamond composite sheet of design model 1308 is 13.00mm × 8.00mm. The amplitude of the ripple wavy structure is 0.3mm and the wavelength is 1mm. The height of the cemented carbide substrate and the gradient layer bonding interface from the crest to the trough is 0.3mm, wherein the crest is 0.15mm high, and the height of the cemented carbide substrate from the crest to the lower bottom surface is 5.5mm. The upper and lower ripple spacing of the upper layer of the gradient layer is a gradual change of 0.3mm to 0.4mm from the crest to the trough, and the upper and lower ripple spacing of each layer except the top layer is 0.4mm. The height of the polycrystalline diamond layer and the gradient layer bonding interface from the crest to the trough is 0.2mm, wherein the crest is 0.05mm high, and the height of the polycrystalline diamond layer from the crest to the upper top surface is 0.6mm.

[0050] The cemented carbide substrate is made of YG13 (WC-13wt%Co) alloy, in which the mass fractions of WC and Co are WC87% and Co13%, and 5 gradient layers are set. The volume content of diamond in each layer from bottom to top is 15%, 30%, 45%, 60%, and 75%, respectively, and the volume content of YG13 in each corresponding gradient layer is 85%, 65%, 55%, 40%, and 25%, respectively. The particle size of YG13 pre-alloyed powder is 40-50μm, and the particle size of diamond powder is 40-50μm.

[0051] The production process is as follows:

[0052] The first step: take an appropriate amount of diamond powder and YG15 pre-alloyed powder; mix them according to the set proportions of the polycrystalline diamond layer and each gradient layer, place the mixed powder in an internal mixer at 160°C for internal mixing, add a certain proportion of special binder, the mass ratio of the special binder to the powder is 1:10, wherein the mass fractions of PW, PMMA, EVA, LDPE, ESO, and stearic acid are 31%, 22%, 22%, 18%, 6%, and 1%, respectively, and internal mixing for 100 minutes, then send the internal mixing feed into a granulator for granulation to obtain a molding material;

[0053] Step 2: Model the five gradient layers, the polycrystalline diamond layer, and the support structure of the gradient layer in the computer, assemble and slice the model files using slicing software, and import the final seven slice files into the pellet FDM printer respectively;

[0054] Step 3: Put the molding material and the water-soluble support material PVA (polyvinyl alcohol) into the two feed hoppers of the dual-extrusion dual-nozzle granular FDM printer respectively, and obtain the gradient layer green body and polycrystalline diamond layer green body with support structure after printing. Set the particle printing parameters: the nozzle diameter used for molding material printing is 0.6mm, the layer height is 0.1mm, the extrusion rate is 40mm / s, and the extrusion flow rate is 130%; the nozzle diameter used for PVA printing is 0.8mm, the layer height is 0.6mm, the extrusion rate is 150mm / s, and the extrusion flow rate is 150%;

[0055] Step 4: placing the gradient layer green body containing the support structure in a beaker filled with water and heating it in a water bath at 80°C to dissolve the support, and after the support is completely dissolved, obtaining the gradient layer green body with the support removed;

[0056] Step 5: Place the printed green sheets in a metal cup in order and put them into a debinding furnace for debinding. The debinding process parameters are: in the first stage, the temperature is increased to 150°C at a heating rate of 8°C / min and kept for 90 minutes. In the second stage, the temperature is increased to 400°C at a heating rate of 4°C / min and kept for 60 minutes. In the third stage, the temperature is increased to 500°C at a heating rate of 2°C / min and kept for 100 minutes. The atmosphere is hydrogen (H2) and the hydrogen flow rate is 4L / min.

[0057] Step 6: Place the degreased sample and cemented carbide substrate into a six-sided hydraulic press, increase the pressure to 5.5 GPa, increase the temperature to 1500°C, and maintain the pressure and temperature for 500 seconds, then stop heating, reduce the pressure, and make the equipment temperature reach room temperature. After the pressure drops to standard atmospheric pressure, take out the polycrystalline diamond composite sheet with a ripple-shaped gradient layer from the six-sided hydraulic press. The comparison results of the residual stress of the composite sheet in the above embodiment and the maximum residual tensile stress of the ordinary composite sheet are shown in Table 1 below.

[0058] Table 1 Finite element analysis results of the maximum residual tensile stress in the composite sheet

[0059] Maximum tensile stress Radial stress(GPa) Axial stress (GPa) Shear stress(GPa) Ordinary composite film 1.52 1.46 1.02 Example 1 0.75 0.35 0.32 Example 2 0.8 0.42 0.38

[0060] Comparative Example:

[0061] In the comparative example, only one experimental parameter was changed, and other experimental conditions were the same as those in Example 1. The comparison results are shown in Table 2 below.

[0062] Table 2 Comparative experimental results

[0063]

[0064]

Claims

1. A method for preparing a polycrystalline diamond compact having a rippled wavy gradient layer, characterized in that: Diamond powder and a binder are mixed and granulated to obtain polycrystalline diamond layer granules; diamond powder, WC-Co alloy powder and a binder are respectively mixed and granulated according to the design components of each layer in the ripple wavy gradient layer to obtain N groups of ripple wavy gradient layer granules; the polycrystalline diamond layer granules are then subjected to fused deposition molding 3D printing to obtain a polycrystalline diamond layer green body; PVA is used as a support layer material; PVA and N groups of ripple wavy gradient layer granules are alternately printed layer by layer to obtain a ripple wavy gradient layer green body A with a support structure; the ripple wavy gradient layer green body with a support structure is removed from the support structure to obtain a ripple wavy gradient layer green body B; the ripple wavy gradient layer green body B and the polycrystalline diamond layer green body are assembled into one to obtain a composite green body; the composite green body is degreased to obtain a degreased composite green body; the degreased composite green body is assembled with a cemented carbide substrate and subjected to high temperature and high pressure synthesis to obtain a polycrystalline diamond composite sheet; The polycrystalline diamond composite sheet is composed of a cemented carbide substrate, a multi-layer ripple wavy gradient layer, and a polycrystalline diamond layer from bottom to top. In the ripple wavy gradient layer, the content of polycrystalline diamond increases from bottom to top, and the content of cemented carbide decreases from bottom to top. In the ripple wavy gradient layer, the amplitude of the ripple wavy structure is 0.2~0.6mm, the wavelength is 1~2mm, the upper and lower ripple spacing in the top layer is set to a gradient of (t / 2~t)mm~tmm from the peak to the trough, and the upper and lower ripple spacings of the remaining layers are all tmm, where t is 0.05~0.

4.

2. The method for preparing a polycrystalline diamond compact having a rippled wave gradient layer according to claim 1, characterized in that: The particle size of the diamond powder is 0.5-100 μm, and the particle size of the WC-Co alloy powder is 0.5-150 μm; The binders in the polycrystalline diamond layer granules and the N-group ripple wave gradient layer granules are composed of the following by mass percentage: paraffin 8-35%, polymethyl methacrylate 20-26%, ethylene-vinyl acetate copolymer 20-26%, polyethylene 18-24%, epoxidized soybean oil 3-8%, and stearic acid 1-3%; In the polycrystalline diamond layer granules, the mass ratio of binder to diamond powder is 1:2-20; In the N groups of ripple wave gradient layer particles, the mass ratio of binder: (diamond powder+WC-Co alloy powder) is 1:2-20.

3. The method for preparing a polycrystalline diamond compact having a rippled wave gradient layer according to claim 1, characterized in that: The diamond powder and the binder are mixed and kneaded at 150°C to 350°C for 60 to 120 minutes, and granulated to obtain polycrystalline diamond layer granules; According to the designed components of each layer in the ripple wave gradient layer, diamond powder, WC-Co alloy powder and binder are respectively mixed at 150°C-350°C for 60-120 minutes and granulated to obtain N groups of ripple wave gradient layer granules.

4. The method for preparing a polycrystalline diamond compact having a rippled wave gradient layer according to claim 1, characterized in that: In the process of obtaining a polycrystalline diamond layer green body by fused deposition modeling 3D printing, the nozzle diameter used is 0.2~4mm, the layer height is 0.05~2mm, the extrusion rate is 2~200mm / s, and the extrusion flow rate is 100~180%; In the process of alternately printing PVA and N groups of ripple wavy gradient layer granules layer by layer to obtain the ripple wavy gradient layer green body A with a support structure, when printing PVA, the nozzle diameter used is 0.4~0.8mm, the layer height is 0.2~0.4mm, the extrusion rate is 100~200mm / s, and the extrusion flow rate is 120~180%. When printing N groups of ripple wavy gradient layer granules, the nozzle diameter used is 0.2~4mm, the layer height is 0.05~2mm, the extrusion rate is 2~200mm / s, and the extrusion flow rate is 100~180%.

5. The method for preparing a polycrystalline diamond compact having a rippled wave gradient layer according to claim 1, characterized in that: The degreasing is carried out in a hydrogen atmosphere, the hydrogen flow rate during the degreasing is 3-5 L / min, and the heating program during the degreasing is: firstly, the temperature is increased from room temperature to 100-150°C at a heating rate of 5-10°C / min, and the temperature is kept for 75-100 minutes; then, the temperature is increased to 350-400°C at a heating rate of 2-6°C / min, and the temperature is kept for 45-60 minutes; then, the temperature is increased to 500-550°C at a heating rate of 1-5°C / min, and the temperature is kept for 90-120 minutes; The pressure of the high temperature and high pressure synthesis is 2-8.5 GPa, the temperature of the high temperature and high pressure synthesis is 1200-1850° C., and the time of the high temperature and high pressure synthesis is 300-1000 s.

6. The method for preparing a polycrystalline diamond compact having a rippled wave gradient layer according to claim 1, characterized in that: The cemented carbide in the cemented carbide substrate and the rippled wave gradient layer is Co-WC, wherein the mass fraction of Co is 5-25%, and the mass fraction of WC is 75-95%.

7. The method for preparing a polycrystalline diamond compact having a rippled wave gradient layer according to claim 1, characterized in that: The ripple wave gradient layer is divided into n layers, and n is 3 to 16 layers.

8. The method for preparing a polycrystalline diamond compact having a rippled wave gradient layer according to claim 1, characterized in that: In the ripple-shaped gradient layer, the volume fraction of polycrystalline diamond in the bottom layer is 5-15%, and then from the second bottom layer to the top layer, the volume fraction increases by 5-30% per layer; the volume fraction of polycrystalline diamond in the top layer is 85-95%, and the volume fraction of cemented carbide in the bottom layer is 85-95%, and then from the second bottom layer to the top layer, the volume fraction decreases by 5-30% per layer.

9. The method for preparing a polycrystalline diamond compact having a rippled wave gradient layer according to claim 1, characterized in that: The top surface of the cemented carbide substrate and the bottom surface of the polycrystalline diamond layer are both in a ripple wave shape.

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