A diamond / cemented carbide composite tooth with a double gradient structure and a preparation method thereof

Abstract

This invention provides a diamond / hard alloy composite tooth with a dual-gradient structure and its preparation method. The diamond / hard alloy composite tooth, from top to bottom along the axial direction, consists of a polycrystalline diamond layer, a diamond / hard alloy gradient transition layer, and a gradient hard alloy substrate. In the diamond / hard alloy gradient transition layer, the content of polycrystalline diamond decreases sequentially from the polycrystalline diamond layer to the hard alloy substrate, while the content of hard alloy increases sequentially. The gradient hard alloy substrate consists of several hard alloy layers arranged coaxially in a nested configuration with different WC and Co ratios, with the WC content decreasing and the Co content increasing sequentially from the outermost to the innermost layer. This invention achieves a continuous transition of material components between diamond and hard alloy, and within the hard alloy substrate, reducing residual stress at the composite interface and improving the impact toughness of the composite tooth; it significantly improves the overall performance and service life of the diamond / hard alloy composite tooth.

Description

Technical Field

[0001] This invention belongs to the field of diamond / hard alloy composite tooth preparation technology, specifically relating to a diamond / hard alloy composite tooth with a dual gradient structure and its preparation method. Background Technology

[0002] Polycrystalline diamond composite (PDC) is an ultra-hard composite material made by sintering polycrystalline diamond (PCD) micro powder and cemented carbide substrate under high temperature and pressure. It combines the high hardness and high wear resistance of diamond with the good toughness and weldability of cemented carbide and is widely used in the oil and gas drilling industry.

[0003] Due to the significant difference in thermal expansion coefficients between the diamond layer and the cemented carbide substrate, large residual stresses are easily generated at the composite interface, leading to fracture, wear, and delamination of PDC teeth during use. In existing technologies, an effective method to reduce residual stress at the composite interface is to incorporate a gradient transition layer between the diamond layer and the cemented carbide substrate, addressing the issue of interlayer physical property compatibility through a gradual transition of material components.

[0004] In gradient-structured PDC teeth, although the cemented carbide substrate possesses good overall toughness, its internal compositional structure lacking a gradient distribution makes it prone to fracture under strong impact loads. A single interface gradient design cannot optimize the internal stress distribution of the entire cemented carbide matrix. Therefore, a diamond-carbide composite tooth design is needed that can simultaneously address the residual stress at the composite interface and improve the impact resistance of the cemented carbide substrate. Summary of the Invention

[0005] To address the problem that existing technologies cannot simultaneously reduce residual stress at the composite interface and improve the impact resistance of the cemented carbide substrate, the first objective of this invention is to provide a diamond / cemented carbide composite tooth with a dual-gradient structure. This composite tooth has a dual-gradient structure in which the diamond content decreases layer by layer from the top to the bottom while the cemented carbide content increases layer by layer, and the WC content of the cemented carbide substrate decreases layer by layer from the outer to the inner layer while the Co content increases layer by layer. This simultaneously solves the problems of easy delamination of the diamond layer and easy breakage of the cemented carbide substrate during the operation of PDC teeth.

[0006] The second objective of this invention is to provide a method for preparing diamond / hard alloy composite teeth with a dual gradient structure. This method uses the fused deposition modeling process in 3D printing, which can precisely control parameters such as the proportion and layer thickness of each component in the gradient layer, achieve large-scale printing, and significantly reduce production costs.

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

[0008] The present invention provides a diamond / hard alloy composite tooth with a dual gradient structure, wherein the diamond / hard alloy composite tooth is composed of a polycrystalline diamond layer, a diamond / hard alloy gradient transition layer and a gradient hard alloy substrate along the axial direction from top to bottom;

[0009] In the diamond / hard alloy gradient transition layer, the content of polycrystalline diamond decreases sequentially and the content of hard alloy increases sequentially along the direction from the polycrystalline diamond layer to the hard alloy substrate.

[0010] The gradient cemented carbide substrate is composed of several cemented carbide layers arranged in a coaxial nested manner with different WC and Co ratios. From the outer layer to the inner layer, the WC content decreases layer by layer, and the Co content increases layer by layer.

[0011] The diamond / hard alloy composite tooth with a dual-gradient structure provided by this invention achieves two key benefits. First, it allows for a gradual transition in performance between the diamond layer and the hard alloy substrate through a multi-layer gradient, resulting in smoother stress changes and reduced residual tensile stress between layers. Second, the volume fraction of WC in the outer layer of the hard alloy substrate is greater than that of Co, giving the outer layer higher hardness. The inner layer has a higher Co content, ensuring that the hard alloy substrate has high toughness and will not easily break during rock crushing. The gradual gradient of component content from the outer layer to the inner layer ensures uniform load transfer within the hard alloy substrate, improving its impact resistance.

[0012] In a preferred embodiment, the diamond / hard alloy composite tooth includes an upper hemisphere and a lower cylinder arranged coaxially; the maximum outer diameter of the upper hemisphere is equal to the outer diameter of the lower cylinder, together forming an integrated upper and lower combined composite tooth configuration; wherein the polycrystalline diamond layer and the diamond / hard alloy gradient transition layer are only composed of concentric spherical shells, while the overall structure of the gradient hard alloy substrate is composed of a hemispherical segment and a lower coaxially connected cylinder.

[0013] In this invention, since the polycrystalline diamond layer has the characteristics of high hardness but low toughness, it is set as a thin spherical shell as a wear-resistant working layer. This can save material costs and avoid brittle failure caused by excessive layer thickness. At the same time, the diamond / hard alloy gradient transition layer is a spherical shell structure, and a substrate with a composite shape of spherical shell and cylinder is used, so that the shape between the transition layer and the substrate can be naturally transitioned, thereby avoiding stress concentration.

[0014] As a preferred embodiment, the diamond / hard alloy gradient transition layer is composed of several concentric spherical shells. The volume fraction of polycrystalline diamond is 5-95%, with 80-95% in the top layer and 5-20% in the bottom layer. From the top layer to the bottom layer, the volume fraction of polycrystalline diamond decreases by 5-25% layer by layer. In the diamond / hard alloy gradient transition layer, the volume fraction of hard alloy is 5-95%, with 5-20% in the top layer and 80-95% in the bottom layer. From the top layer to the bottom layer, the volume fraction of hard alloy increases by 5-25% layer by layer.

[0015] As a preferred embodiment, the cemented carbide in the diamond / hard alloy gradient transition layer is Co-WC, wherein the volume fraction of Co is 3% to 11%, and the Co content in the diamond / hard alloy gradient transition layer is equal to the Co content of the outermost layer of the gradient cemented carbide substrate.

[0016] As a preferred embodiment, the diamond / hard alloy gradient transition layer has 4 to 15 layers. If the number of layers is too small, the compositional differences between the gradient layers are large, making it difficult to achieve a smooth transition in performance; if the number of layers is too large, the precision requirements of the printer are higher, and the printing cost is significantly increased.

[0017] As a preferred embodiment, the thickness of each layer in the diamond / hard alloy gradient transition layer is 0.05–0.2 mm, and the total thickness is 0.2–3 mm. In this invention, the thickness distribution of each gradient layer can be either uniform or non-uniform.

[0018] As a preferred embodiment, in the gradient cemented carbide substrate, the volume fraction of WC is 65-97%, with the volume fraction in the outermost layer being 89-97% and the volume fraction in the innermost layer being 65-81%, and the volume fraction of WC decreasing by 1-10% layer by layer from the outermost to the innermost layer; in the gradient cemented carbide substrate, the volume fraction of Co is 3-35%, with the volume fraction in the outermost layer being 3-11% and the volume fraction in the innermost layer being 19-35%, and the volume fraction of Co increasing by 1-10% layer by layer from the outermost to the innermost layer.

[0019] In a further preferred embodiment, the cemented carbide layer with a Co volume fraction of 11% in the gradient cemented carbide substrate is bonded to the bottom layer of the diamond / cemented carbide gradient transition layer. Experiments have shown that the cemented carbide layer with 11% Co content exhibits the best bonding performance with the diamond / cemented carbide gradient transition layer, and bonding it to the bottom layer of the diamond / cemented carbide gradient transition layer results in the optimal interfacial bonding performance.

[0020] As a preferred embodiment, the gradient cemented carbide substrate contains 3 to 15 coaxially nested cemented carbide layers from the inside out. If the number of layers is too small, the impact resistance of the cemented carbide cannot be guaranteed.

[0021] As a preferred embodiment, the thickness of each cemented carbide layer is 0.05 to 4 mm.

[0022] In this invention, the thickness of each layer of the cemented carbide layer can be distributed either uniformly or non-uniformly.

[0023] In a further preferred embodiment, the thickness of the cemented carbide layer decreases progressively from the inside out. The outer cemented carbide gradient layer has a low Co content and a high WC content, exhibiting high hardness but low toughness. Setting the gradient layer to have a progressively decreasing thickness from the outside in optimizes stress distribution. The inner layer is relatively tougher and thicker, effectively buffering and absorbing impact energy. Furthermore, the outer layer has a high WC content and high cost; making the outer layer thinner saves material costs.

[0024] As a preferred embodiment, in the gradient cemented carbide substrate, the maximum outer diameter of the hemispherical segment is smaller than the outer diameter of the cylinder. The upper end face of the cylinder extends radially outward beyond the bottom surface of the hemispherical segment, forming a radial step that mates with the lower end of the spherical shell of the diamond / cemented carbide gradient transition layer. This structure avoids direct bonding between the gradient layer (with a volume fraction of less than 11%) in the cemented carbide substrate and the diamond / cemented carbide gradient transition layer, which would otherwise result in poor interfacial performance.

[0025] In a further preferred embodiment, the hard alloy layer of the gradient hard alloy substrate consists of a central core, an intermediate nested layer, and an outer nested layer from the inside out. The central core is composed of a solid cylinder and a coaxially connected hemispherical core. The intermediate nested layer is composed of multiple layers of solid cylindrical tubes nested outwards and a spherical shell coaxially connected to the solid cylindrical tubes with the same thickness. The outer nested layer is composed of solid cylindrical tubes nested outwards.

[0026] In a further optimized configuration, the thickness of each solid cylindrical tube in the outer nesting layer is 0.05–1 mm, while the thickness of each solid cylindrical tube in the middle nesting layer is ≥1 mm. Experiments have shown that this optimized thickness setting results in composite teeth with excellent wear resistance and low cost.

[0027] Further preferred, the volume fraction of Co in the outer nested layer is <11%, and the volume fraction of Co in the middle nested layer is ≥11%. With this preferred composition setting, the bonding effect between the cemented carbide layer and the diamond layer is optimal.

[0028] In a further preferred embodiment, the curvature of the diamond / hard alloy gradient layer gradually decreases from the top to the bottom, and the curvature of each spherical shell of the gradient hard alloy substrate is the same. In this invention, the gradual decrease in curvature of the diamond / hard alloy gradient layer from the top to the bottom buffers stress, coordinates deformation, and suppresses stress concentration and delamination; while the uniform curvature of each spherical shell of the gradient hard alloy substrate ensures the uniformity and stability of the stress distribution inside the substrate, avoiding stress singularities caused by geometric abrupt changes.

[0029] This invention also provides a method for preparing diamond / hard alloy composite teeth with a dual-gradient structure. According to the composition of the gradient hard alloy substrate, WC powder, Co powder, and binder A are mixed to obtain n groups of gradient hard alloy mixtures with different proportions. The n groups of gradient hard alloy mixtures are then subjected to mixing, granulation, and wire drawing to obtain n groups of gradient hard alloy wires. The n groups of gradient hard alloy wires are then processed layer-by-layer printing to obtain a gradient hard alloy green blank. According to the composition of the diamond / hard alloy gradient transition layer, polycrystalline diamond powder, WC-Co hard alloy powder, and binder B are mixed to obtain m groups of diamond / hard alloy gradient transition layer mixtures with different proportions. The m groups of diamond / hard alloy gradient transition layer mixtures are then subjected to mixing, granulation, and wire drawing to obtain m groups of diamond / hard alloy gradient transition layer wires. The m groups of diamond / hard alloy gradient transition layer wires are then processed layer-by-layer printing to obtain a gradient hard alloy green blank. A diamond / hard alloy transition layer green blank is prepared by printing. Polycrystalline diamond and binder C are mixed to obtain a polycrystalline diamond layer mixture. The polycrystalline diamond layer mixture is then subjected to mixing, granulation, and wire drawing to obtain polycrystalline diamond layer wire. The polycrystalline diamond layer wire is then printed to obtain a polycrystalline diamond green blank. The gradient hard alloy green blank is degreased to obtain a gradient hard alloy degreased blank. The gradient hard alloy degreased blank is then sintered to obtain a gradient hard alloy sintered blank. The diamond / hard alloy transition layer green blank and the polycrystalline diamond green blank are degreased to obtain a diamond / hard alloy transition layer degreased blank and a polycrystalline diamond degreased blank, respectively. Then, according to the structure of the diamond / hard alloy composite tooth, the gradient hard alloy sintered blank, the diamond / hard alloy transition layer degreased blank, and the polycrystalline diamond degreased blank are assembled in a bottom-to-top order and then synthesized under high temperature and high pressure to obtain the diamond / hard alloy composite tooth.

[0030] In this invention, the gradient cemented carbide substrate is first sintered, and then assembled with the diamond / cemented carbide transition layer degreased blank and the polycrystalline diamond degreased blank and then subjected to high temperature and high pressure synthesis. This can adapt to the conventional sintering densification of cemented carbide and the high pressure bonding conditions of diamond layer respectively, effectively suppress the excessive migration of Co, ensure the geometric accuracy and gradient structure of the substrate, and achieve reliable bonding between interfaces.

[0031] In the preparation method of this invention, the uniformity of the components of the melt extruded material is ensured through processes such as mixing, granulation, drawing, and printing. The minimum layer thickness that 3D printing technology can print is 0.05 mm, which can realize multi-layer transition between composite interfaces, with small differences in components between layers and better bonding effect.

[0032] As a preferred embodiment, the polydiamond powder has a particle size of 1–50 μm, the WC powder has a particle size of 5–200 μm, and the Co powder has a particle size of 1–100 μm.

[0033] As a preferred embodiment, the adhesive A, by weight percentage, comprises the following components: 20-45% polyethylene (LDPE), 20-35% paraffin wax (PW), 8-12% microcrystalline wax, 8-12% polymethyl methacrylate (PMMA), 12-15% ethylene-vinyl acetate copolymer (EVA), 2-3% epoxidized soybean oil (ESO), 1-3% stearic acid (SA), and 1-2% butylated hydroxytoluene (BHT).

[0034] In the binder component A, LDPE and PMMA both serve as skeleton components, providing room temperature strength for the green body and improving shape retention during the high-temperature degreasing stage; PW, as a flow modifier, acts as a low-temperature removal component, significantly reducing melt viscosity and improving flowability during printing; EVA, as a wetting agent, improves the interfacial wettability between the binder and WC-Co powder, regulating melt rheological behavior; ESO, as a plasticizer and lubricant, improves processing flowability and mixing uniformity; SA, as a surfactant and lubricant, reduces friction during molding; microcrystalline wax is added to improve low-temperature degreasing behavior, and BHT is added to prevent oxidative discoloration of the binder during the high-temperature degreasing stage and control residual carbon.

[0035] As a preferred embodiment, in the n-group gradient cemented carbide mixture, the total mass ratio of WC powder and Co powder to the mass ratio of binder A is 1~6:1.

[0036] As a preferred embodiment, when n groups of gradient cemented carbide mixtures are sequentially subjected to mixing, granulation, and wire drawing to obtain n groups of gradient cemented carbide wires, the mixing temperature is controlled at 160–200℃, the rotation speed at 30–60 r / min, and the time at 60–90 min; the granulation temperature is controlled at 160–200℃, the rotation speed at 30–60 r / min; the wire drawing temperature is controlled at 180–220℃, and the wire drawing machine rotation speed at 40–50 rpm; the diameter of the n groups of gradient cemented carbide wires is 1.70–1.85 mm.

[0037] As a preferred embodiment, when the n groups of gradient cemented carbide wires are printed to obtain gradient cemented carbide green blanks, the printing layer height is controlled to be 0.05-2 mm, the nozzle diameter to be 0.2-0.4 mm, the nozzle temperature to be 180-220°C, the printing speed to be 50-150 mm / s, the printing temperature to be 80-120°C, and the extrusion flow rate to be 100-200%.

[0038] As a preferred embodiment, the adhesive B, by weight percentage, comprises the following components: 25-35% polyethylene (LDPE), 20-35% polymethyl methacrylate (PMMA), 15-25% ethylene-vinyl acetate copolymer (EVA), 10-12% paraffin wax (PW), 3-5% vinyl bis-stearamide (EBS), 2-3% stearic acid (SA), and 1-2% dioctyl phthalate (DOP).

[0039] In the binder component B, LDPE and PMMA serve as the main skeleton components; EVA acts as a wetting agent and adhesion promoter, significantly improving the wettability of the binder and powder, and enhancing the uniformity and flowability of the feed; PW acts as a filler; EBS acts as a lubricant and dispersant, possessing excellent lubrication properties, which can improve feed flowability and powder dispersion uniformity, and reduce powder agglomeration; SA acts as a surfactant and lubricant, reducing the tendency of powder agglomeration; and DOP acts as a plasticizer, improving the flowability and flexibility of the feed.

[0040] As a preferred embodiment, in the m-group diamond / hard alloy gradient transition layer mixture, the total mass ratio of polycrystalline diamond powder and hard alloy powder to the mass ratio of binder B is 1~8:1.

[0041] As a preferred embodiment, when obtaining m-group diamond / hard alloy gradient transition layer wires by mixing, granulating, and drawing the m-group diamond / hard alloy gradient transition layer mixtures, the mixing temperature is controlled at 160–200℃, the rotation speed at 30–60 r / min, and the time at 60–90 min; the granulation temperature is controlled at 160–200℃, the rotation speed at 30–60 r / min; the drawing temperature is controlled at 180–220℃, and the drawing machine rotation speed at 40–50 rpm. The diameter of the m-group diamond / hard alloy gradient transition layer wires is 1.70–1.85 mm.

[0042] As a preferred embodiment, when preparing a diamond / hard alloy transition layer green blank by printing m groups of diamond / hard alloy gradient transition layer wires, the printing layer height is controlled to be 0.05-2 mm, the nozzle diameter to be 0.2-0.4 mm, the nozzle temperature to be 180-220℃, the printing speed to be 50-150 mm / s, the printing temperature to be 80-120℃, and the extrusion flow rate to be 100-200%.

[0043] As a preferred embodiment, the adhesive C, by mass percentage, comprises the following components: 15-25% polyethylene (LDPE), 25-40% paraffin wax (PW), 12-20% ethylene-vinyl acetate copolymer (EVA), 8-15% polyethylene glycol (PEG), 2-4% stearic acid (SA), 3-8% microcrystalline wax, 2-5% epoxidized soybean oil (ESO), and 0.5-1.5% butylated hydroxytoluene (BHT).

[0044] As a preferred embodiment, in the polycrystalline diamond layer mixture, the binder C: polycrystalline diamond powder ratio is 1:1 to 10 by mass.

[0045] As a preferred embodiment, when obtaining polycrystalline diamond layer wire by mixing, granulation, and drawing the polycrystalline diamond layer mixture, the mixing temperature is controlled at 160-200℃, the rotation speed at 30-60 r / min, and the time at 60-90 min; the granulation temperature is controlled at 160-200℃, the rotation speed at 30-60 r / min; the drawing temperature is controlled at 180-220℃, and the drawing machine rotation speed at 40-50 rpm; the diameter of the polycrystalline diamond layer wire is 1.70-1.85 mm.

[0046] As a preferred embodiment, when the polycrystalline diamond layer filament is printed to obtain a polycrystalline diamond green blank, the printing layer height is controlled to be 0.05-2 mm, the nozzle diameter to be 0.2-0.4 mm, the nozzle temperature to be 180-220°C, the printing speed to be 50-150 mm / s, the printing temperature to be 80-120°C, and the extrusion flow rate to be 100-200%.

[0047] During the actual printing process of each part, geometric models of polycrystalline diamond layer, diamond / hard alloy gradient transition layer, and gradient hard alloy substrate were created in 3D modeling software and exported as STL files. Slicing software was used to slice each model and the generated slice files were imported into the 3D printer. Then, different filaments were placed into the printer feed port, the printing parameters were set, and the equipment was started to print, obtaining gradient hard alloy green blanks, diamond / hard alloy gradient transition layer green blanks, and polycrystalline diamond green blanks.

[0048] As a preferred embodiment, the debinding process for gradient cemented carbide green blanks, diamond / cemented carbide transition layer green blanks, and polycrystalline diamond green blanks is as follows: first, the temperature is increased from room temperature to 120–160°C at a heating rate of 4–10°C / min, and held for 60–120 min; then, the temperature is increased to 250–300°C at a heating rate of 3–8°C / min, and held for 90–120 min; next, the temperature is increased to 350–450°C at a heating rate of 2–6°C / min, and held for 60–90 min; finally, the temperature is increased to 550–600°C at a heating rate of 1–3°C / min, and held for 90–120 min. In this invention, each printed green blank is placed in a vacuum debinding furnace, and debinding is performed using gradient heating technology, which can significantly improve the structural integrity of the green blank while ensuring that the binder is fully removed.

[0049] As a preferred embodiment, the degreased gradient cemented carbide blank is placed in a hot isostatic pressing furnace for sintering. The sintering process involves first heating to 1300–1500°C and holding the sintering at this temperature under vacuum for 60–90 minutes; then, using argon as the pressure medium, hot isostatic pressing is performed at a pressing pressure of 6–8 MPa for 30–60 minutes. In the sintering process of this invention, the degreased gradient cemented carbide blank is first held under vacuum for a period of time. During this stage, preliminary densification is achieved through the rearrangement and dissolution-precipitation process of WC particles in the liquid phase. Subsequently, argon is used as the pressure medium, and a small amount of argon is introduced into the furnace for partial pressure control to adjust the carbon content of the cemented carbide and suppress surface depletion. Under this pressure, the residual micropores inside the material are closed, allowing the cemented carbide to reach a density close to the theoretical value, while obtaining a gradient cemented carbide substrate that conforms to the composition design ratio of this invention.

[0050] As a preferred embodiment, the high-temperature and high-pressure synthesis is controlled at a pressure of 5–8 GPa, a temperature of 1400–1800 °C, and a time of 10–20 min.

[0051] Beneficial effects

[0052] The diamond / carbide composite tooth with a dual gradient structure provided by the present invention has a diamond content that decreases layer by layer from top to bottom while the carbide content increases layer by layer, and a carbide substrate with a WC content that decreases layer by layer from the outer layer to the inner layer while the Co content increases layer by layer. By utilizing the gradient changes of the two components between the two phase interfaces and inside the substrate, the residual stress at the composite interface and the impact toughness of the composite tooth are simultaneously reduced.

[0053] This invention uses melt extrusion molding 3D printing technology to prepare dual-gradient diamond / hard alloy composite teeth. It can uniformly print multi-layer linear gradient transition layers and nested gradient transition layer structures, precisely control parameters such as layer height and layer thickness, and achieve mass production, significantly reducing production costs. Attached Figure Description

[0054] Figure 1 This is a schematic diagram of the structure of the dual-gradient diamond / hard alloy composite tooth of the present invention; 1-polycrystalline diamond layer, 2-diamond / hard alloy gradient structure transition layer, 3-gradient hard alloy substrate.

[0055] Figure 2 The images show a cross-sectional view and a bottom view of the dual-gradient diamond / hard alloy composite tooth prepared according to specific embodiment 1 of the present invention.

[0056] Figure 3 The images show a cross-sectional view and a bottom view of the dual-gradient diamond / hard alloy composite tooth prepared according to specific embodiment 2 of the present invention. Detailed Implementation

[0057] To better understand the above-mentioned objects, features, and advantages of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of this application can be combined with each other. Many specific details are set forth in the following description to provide a thorough understanding of the present invention; however, the present invention may also be implemented in other ways different from those described herein. Therefore, the present invention is not limited to the specific embodiments disclosed in the following specification.

[0058] Example 1

[0059] The diameter × height dimensions of the dual-gradient diamond / carbide composite tooth are designed to be 18.00 mm × 20 mm; the thickness of the polycrystalline diamond layer is 1 mm.

[0060] The diamond / hard alloy gradient transition layer consists of 5 layers, each with a thickness of 0.2 mm, for a total thickness of 1 mm. The volume fractions of each component in the diamond / hard alloy gradient transition layer, from the polycrystalline diamond layer to the gradient hard alloy substrate, are as follows:

[0061] 80% PCD + 20% YG11;

[0062] 60% PCD + 40% YG11;

[0063] 40% PCD + 60% YG11;

[0064] 20% PCD + 80% YG11;

[0065] 10% PCD + 90% YG11.

[0066] The gradient cemented carbide substrate has three layers, with a uniform layer thickness (or diameter) of 3 mm per layer. The volume fraction of each component in the gradient cemented carbide substrate, from the outermost layer to the innermost layer, is as follows:

[0067] The first layer contains 89% WC and 11% Co.

[0068] The second layer is 85% WC + 15% Co;

[0069] The third layer contains 81% WC and 19% Co.

[0070] The polycrystalline diamond powder has a particle size of 50 μm, the WC powder has a particle size of 100 μm, and the Co powder has a particle size of 80 μm.

[0071] Adhesive A is composed of the following components: 35% polyethylene (LDPE), 25% paraffin (PW), 10% microcrystalline wax, 10% polymethyl methacrylate (PMMA), 12% ethylene-vinyl acetate copolymer (EVA), 3% epoxidized soybean oil (ESO), 3% stearic acid (SA), and 2% butylated hydroxytoluene (BHT).

[0072] Adhesive B is composed of the following components: 35% polyethylene (LDPE), 25% polymethyl methacrylate (PMMA), 20% ethylene-vinyl acetate copolymer (EVA), 10% paraffin wax (PW), 5% vinyl bis-stearamide (EBS), 3% stearic acid (SA), and 2% dioctyl phthalate (DOP).

[0073] Adhesive C is composed of the following components: 25% polyethylene (LDPE), 30% paraffin (PW), 20% ethylene-vinyl acetate copolymer (EVA), 15% polyethylene glycol (PEG), 2% stearic acid (SA), 4% microcrystalline wax, 3% epoxidized soybean oil (ESO), and 1% butylated hydroxytoluene (BHT).

[0074] Binder A: Hard alloy powder mass ratio = 1:1;

[0075] Binder B: (polycrystalline diamond powder + cemented carbide powder) mass ratio = 1:1.5;

[0076] The mass ratio of binder C to polycrystalline diamond powder is 1:2.

[0077] The steps of the method for preparing diamond / hard alloy composite teeth with a dual gradient structure provided in this embodiment are as follows:

[0078] 1) Mixing: According to the design composition ratio of the gradient cemented carbide substrate, WC powder, Co powder, and binder A are prepared and mixed evenly in a mixer to obtain mixture A; according to the design composition ratio of the diamond / cemented carbide gradient transition layer, polycrystalline diamond powder, WC-Co cemented carbide powder, and binder B are prepared and mixed evenly in a mixer to obtain mixture B; according to the design composition ratio of the polycrystalline diamond layer, polycrystalline diamond powder and binder C are prepared and mixed evenly in a mixer to obtain mixture C.

[0079] 2) Internal mixing: Place mixtures A, B and C into an internal mixer and mix for 60 minutes at a temperature of 180℃ and a speed of 45r / min.

[0080] 3) Granulation: Place the granulated material in a granulator and granulate it at a temperature of 190℃ and a rotation speed of 50r / min;

[0081] 4) Wire drawing: The prepared granules A, B and C are placed into the extrusion wire drawing machine respectively, and wire drawing is carried out under the conditions of wire drawing temperature of 200℃ and wire drawing machine speed of 45rpm to obtain 3 groups of gradient cemented carbide wires with different formulation ratios and 5 groups of diamond / cemented carbide gradient transition layer wires and 1 group of polycrystalline diamond layer wires with a diameter of 1.80mm.

[0082] 5) Modeling: Create geometric models of the polycrystalline diamond layer, diamond / hard carbide gradient transition layer and gradient hard carbide substrate in 3D modeling software, and export the model files in STL format; use slicing software to slice each model, and import the generated final slice files into the 3D printer.

[0083] 6) Green printing: Different filaments are placed into the printer feed inlet, and the printing parameters are set as follows: printing layer height is 0.1mm, nozzle diameter is 0.4mm, nozzle temperature is 195℃, printing speed is 100mm / s, printing temperature is 110℃, and extrusion flow rate is 130%. The equipment is started to print, and gradient cemented carbide green blanks, diamond / cemented carbide gradient transition layer green blanks, and polycrystalline diamond green blanks are obtained respectively.

[0084] 7) Degreasing (Sintering): The printed blanks were placed in a vacuum degreasing furnace. The temperature was first increased from room temperature to 130°C at a rate of 8°C / min and held for 75 min. Then the temperature was increased to 270°C at a rate of 6°C / min and held for 90 min. Next, the temperature was increased to 400°C at a rate of 4°C / min and held for 90 min. Finally, the temperature was increased to 580°C at a rate of 2°C / min and held for 90 min. Gradient cemented carbide degreasing blanks, diamond / cemented carbide gradient transition layer degreasing blanks, and polycrystalline diamond degreasing blanks were obtained. The gradient cemented carbide degreasing blanks were placed in a hot isostatic pressing furnace and heated to 1400°C. Vacuum sintering was then carried out for 80 min. Then, argon gas was used as the pressure medium and hot isostatic pressing was performed at a pressing pressure of 7 MPa for 45 min. After sintering, the blanks were cooled with the furnace to obtain gradient structure cemented carbide sintered blanks.

[0085] 8) Assembly and finishing: The gradient cemented carbide substrate sintered blank, the diamond / cemented carbide gradient transition layer degreased blank and the polycrystalline diamond layer degreased blank are assembled in the order from bottom to top; synthesized for 15 min under high temperature and high pressure conditions of 6 GPa and 1600℃, and after finishing, diamond / cemented carbide composite teeth with dual gradient structure are obtained.

[0086] 9) Performance Testing: The prepared diamond / hard alloy composite teeth with a dual-gradient structure were subjected to performance testing. Raman spectroscopy revealed a residual tensile stress of 209 MPa at the interface between the polycrystalline diamond layer and the diamond / hard alloy gradient transition layer, which is only 20%–40% of the residual stress at the interface between the two phases in ordinary PDC teeth. Drop hammer impact testing showed an impact toughness of 13.4 J / cm². 2 It exhibits 20%–30% higher impact toughness than PDC teeth with no gradient structure on the substrate; its drilling performance was analyzed using indoor drilling experiments, with an average drilling speed of 0.56 m / min and a wear rate reduced to 0.01 mm / m.

[0087] Example 2

[0088] The diameter × height dimensions of the dual-gradient diamond / carbide composite tooth are designed to be 16.30 mm × 20.2 mm; the thickness of the polycrystalline diamond layer is 1 mm.

[0089] The diamond / hard alloy gradient transition layer consists of 8 layers, each with a thickness of 0.15 mm, for a total thickness of 1.2 mm. The volume fractions of each component in the diamond / hard alloy gradient transition layer, from the polycrystalline diamond layer to the gradient hard alloy substrate, are as follows:

[0090] The first layer consists of 80% PCD and 20% YG3.

[0091] The second layer consists of 70% PCD and 30% YG3.

[0092] The third layer consists of 60% PCD and 40% YG3.

[0093] The fourth layer is 50% PCD + 50% YG3;

[0094] The fifth layer contains 40% PCD and 60% YG3.

[0095] The sixth layer contains 30% PCD and 70% YG3.

[0096] The seventh layer contains 20% PCD and 80% YG3.

[0097] The eighth layer is 10% PCD + 90% YG3.

[0098] The gradient cemented carbide substrate has 7 layers with unevenly distributed layer thicknesses, ranging from 0.50, 0.80, 1.00, 1.20, 1.35, 1.55, and 1.75 mm from the outermost to the innermost layer. The composition of the gradient cemented carbide substrate from the outermost to the innermost layer is as follows:

[0099] The first layer is 97% WC + 3% Co;

[0100] The second layer is 93% WC + 7% Co;

[0101] The third layer contains 89% WC and 11% Co.

[0102] The fourth layer is 85% WC + 15% Co;

[0103] The fifth layer contains 81% WC and 19% Co.

[0104] The sixth layer contains 77% WC and 23% Co.

[0105] The seventh layer contains 73% WC and 27% Co.

[0106] The particle size of polycrystalline diamond powder is 30 μm, the particle size of WC powder is 80 μm, and the particle size of Co powder is 80 μm.

[0107] Adhesive A is composed of the following components: 36% polyethylene (LDPE), 23% paraffin wax (PW), 12% microcrystalline wax, 10% polymethyl methacrylate (PMMA), 12% ethylene-vinyl acetate copolymer (EVA), 3% epoxidized soybean oil (ESO), 2.5% stearic acid (SA), and 1.5% butylated hydroxytoluene (BHT).

[0108] Adhesive B is composed of the following components: 30% polyethylene (LDPE), 30% polymethyl methacrylate (PMMA), 20% ethylene-vinyl acetate copolymer (EVA), 13% paraffin wax (PW), 3% vinyl bis-stearamide (EBS), 2% stearic acid (SA), and 2% dioctyl phthalate (DOP).

[0109] Adhesive C is composed of the following components: 25% polyethylene (LDPE), 26% paraffin wax (PW), 20% ethylene-vinyl acetate copolymer (EVA), 12% polyethylene glycol (PEG), 4% stearic acid (SA), 8% microcrystalline wax, 3.5% epoxidized soybean oil (ESO), and 1.5% butylated hydroxytoluene (BHT).

[0110] Binder A: Hard alloy powder mass ratio = 1:1;

[0111] Binder B: (polycrystalline diamond powder + cemented carbide powder) mass ratio = 1:2;

[0112] The mass ratio of binder C to polycrystalline diamond powder is 1:2.

[0113] The method for preparing diamond / hard alloy composite teeth with a dual gradient structure provided in this embodiment includes the following steps:

[0114] 1) Mixing: According to the design component ratio of the gradient cemented carbide substrate, WC powder, Co powder, and binder A are prepared and mixed evenly in a mixer to obtain mixture A; according to the design component ratio of the diamond / cemented carbide gradient transition layer, polycrystalline diamond powder, WC-Co cemented carbide powder, and binder B are prepared and mixed evenly in a mixer to obtain mixture B; according to the design ratio of the polycrystalline diamond layer, polycrystalline diamond powder and binder C are prepared and mixed evenly in a mixer to obtain mixture C.

[0115] 2) Internal mixing: Place mixtures A, B and C into an internal mixer and mix for 60 minutes at a temperature of 195℃ and a speed of 60r / min.

[0116] 3) Granulation: Place the granulated material in a granulator and granulate it at a temperature of 195℃ and a rotation speed of 60r / min;

[0117] 4) Wire drawing: The prepared granules A, B and C are placed into an extrusion wire drawing machine and drawn at a wire drawing temperature of 200℃ and a wire drawing machine speed of 50rpm to obtain 7 groups of gradient cemented carbide wires with different formulation ratios, 8 groups of diamond / cemented carbide gradient transition layer wires and 1 group of polycrystalline diamond layer wires with a diameter of 1.80mm.

[0118] 5) Modeling: Create geometric models of the polycrystalline diamond layer, diamond / hard carbide gradient transition layer and gradient hard carbide substrate in 3D modeling software, and export the model files in STL format; use slicing software to slice each model, and import the generated slice files into the 3D printer.

[0119] 6) Green printing: Place different filaments into the printer feed inlet, set the printing parameters as follows: printing layer height 0.05mm, nozzle diameter 0.4mm, nozzle temperature 200℃, printing speed 120mm / s, printing temperature 120℃, extrusion flow rate 150%; start the equipment to print and obtain gradient cemented carbide green blanks, diamond / cemented carbide gradient transition layer green blanks, and polycrystalline diamond green blanks.

[0120] 7) Degreasing (Sintering): The printed blanks were placed in a vacuum degreasing furnace. The temperature was first increased from room temperature to 130°C at a rate of 8°C / min and held for 75 min. Then the temperature was increased to 270°C at a rate of 6°C / min and held for 90 min. Next, the temperature was increased to 400°C at a rate of 4°C / min and held for 90 min. Finally, the temperature was increased to 580°C at a rate of 2°C / min and held for 90 min. Gradient cemented carbide degreasing blanks, diamond / cemented carbide gradient transition layer degreasing blanks, and polycrystalline diamond degreasing blanks were obtained. The gradient cemented carbide degreasing blanks were placed in a hot isostatic pressing furnace and heated to 1400°C. Vacuum sintering was then carried out for 80 min. Then, argon gas was used as the pressure medium and hot isostatic pressing was performed at a pressing pressure of 7 MPa for 45 min. After sintering, the blanks were cooled with the furnace to obtain gradient structure cemented carbide sintered blanks.

[0121] 8) Assembly and finishing: The gradient cemented carbide sintered blank, the diamond / cemented carbide gradient transition layer degreased blank and the polycrystalline diamond layer degreased blank are assembled in the order from bottom to top; they are synthesized for 15 minutes under high temperature and high pressure conditions of 8 GPa and 1800℃, and after finishing, diamond / cemented carbide composite teeth with a double gradient structure are obtained.

[0122] 9) Performance Testing: The prepared diamond / hard alloy composite teeth with a dual-gradient structure were subjected to performance testing. Raman spectroscopy revealed that the residual tensile stress at the interface between the polycrystalline diamond layer and the diamond / hard alloy gradient transition layer was 187 MPa, which is only 15%–35% of the residual stress at the interface between the two phases in ordinary PDC teeth. The impact toughness was measured to be 15.9 J / cm² using a drop hammer impact test. 2The impact toughness is 25% to 40% higher than that of PDC teeth with no gradient structure on the substrate; no fracture or obvious deformation of the cemented carbide substrate was observed during the experiment; its drilling performance was analyzed by indoor drilling test, with an average drilling speed of 0.64 m / min and a wear rate reduced to 0.008 mm / m.

[0123] Comparative Example 1

[0124] The comparative example uses a carburizing / decarburizing method to design the cobalt content gradient in the matrix. The gradient design has limited freedom and cannot precisely control the gradient shape. The transition layer between the polycrystalline diamond and the cemented carbide matrix is ​​a single transition layer without a multi-layer gradient structure, which limits the interface bonding effect and results in relatively large residual tensile stress at the interface. The preparation method is powder metallurgy pressing + sintering, which greatly limits the material distribution uniformity, the number of gradient transition layers, and the thickness of a single layer.

[0125] Comparative Example 2

[0126] Other conditions were the same as in Example 2, except that the cemented carbide substrate did not have a gradient structure, and the substrate composition was 89% WC + 11% Co. The polycrystalline diamond layer and the cemented carbide substrate had the same gradient structure as in Example 2. Using the same 3D printing equipment, and following the same printing settings and debinding sintering conditions as in Example 2, a single-gradient diamond / cemented carbide ball tooth was obtained. The physical properties of the double-gradient diamond / cemented carbide composite tooth obtained in Example 2 and the single-gradient diamond / cemented carbide ball tooth in this comparative example were tested under the same working conditions. The impact toughness of the single-gradient diamond / cemented carbide ball tooth in this comparative example was 10.7 J / cm². 2 Its average drilling speed is 0.45 m / min, and the tool wear rate is 0.015 mm / m, which is significantly lower than that of the dual-gradient diamond / carbide composite tooth prepared in Example 2; and under strong impact conditions, the carbide matrix in this comparative example is prone to fracture.

[0127] Comparative Example 3

[0128] Other conditions were the same as in Example 2, except that there was no gradient structure between the polycrystalline diamond layer and the cemented carbide substrate, and the cemented carbide substrate had 7 gradient transition layers with the same composition as in Example 2. The same 3D printing equipment was used, and the substrate was cured under the same printing settings and debinding sintering conditions as in Example 2 to obtain diamond / cemented carbide ball teeth with a single gradient structure. The interfacial residual stress of the diamond / cemented carbide ball teeth in this comparative example was 395 MPa, which is 2.1 times that of Example 2. Under strong impact, the diamond layer is prone to delamination.

[0129] Comparative Example 4

[0130] Other conditions were the same as in Example 2, except that the binder did not contain BHT (butylated hydroxytoluene), and all other components remained unchanged. Using the same 3D printing equipment, the balls were cured under the same printing settings and debinding / sintering conditions as in Example 2 to obtain a dual-gradient diamond / carbide ball tooth structure. However, during physical property testing, the ball tooth without BHT exhibited a significant performance disadvantage. The impact toughness of the ball tooth in this comparative example was 14.6 J / cm². 2 Its average drilling speed was 0.58 m / min, and the tool wear rate was 0.011 mm / m, which was significantly lower than that of the dual-gradient diamond / carbide composite teeth prepared in Example 2. As a key antioxidant, the absence of BHT can lead to binder oxidation and discoloration during the high-temperature degreasing stage, as well as uncontrolled residual carbon content, ultimately affecting the service life and operational efficiency of the finished ball teeth.

[0131] The above embodiments are for illustrative purposes only and are not intended to limit the invention. Those skilled in the art will recognize that the invention can be modified and varied in many ways. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A diamond / carbide composite tooth with a dual-gradient structure, characterized in that: The diamond / hard alloy composite tooth consists of a polycrystalline diamond layer, a diamond / hard alloy gradient transition layer, and a gradient hard alloy substrate along the axial direction from top to bottom. In the diamond / hard alloy gradient transition layer, the content of polycrystalline diamond decreases sequentially and the content of hard alloy increases sequentially along the direction from the polycrystalline diamond layer to the hard alloy substrate. The gradient cemented carbide substrate is composed of several cemented carbide layers arranged in a coaxial nested manner with different WC and Co ratios. From the outer layer to the inner layer, the WC content decreases layer by layer, and the Co content increases layer by layer.

2. The diamond / carbide composite tooth with a dual-gradient structure according to claim 1, characterized in that: The diamond / hard alloy composite tooth includes an upper hemisphere and a lower cylinder arranged coaxially; the maximum outer diameter of the upper hemisphere is equal to the outer diameter of the lower cylinder, together forming an integrated upper and lower combined composite tooth configuration; wherein the polycrystalline diamond layer and the diamond / hard alloy gradient transition layer are only composed of concentric spherical shells, while the overall structure of the gradient hard alloy substrate is composed of a hemispherical segment and a lower coaxially connected cylinder.

3. A diamond / carbide composite tooth with a dual-gradient structure according to claim 1 or 2, characterized in that: The diamond / hard carbide gradient transition layer consists of several concentric spherical shells. In the diamond / hard carbide gradient transition layer, the volume fraction of polycrystalline diamond is 5-95%, with 80-95% in the top layer and 5-20% in the bottom layer; the volume fraction of polycrystalline diamond decreases by 5-25% layer by layer from the top to the bottom layer. In the diamond / hard carbide gradient transition layer, the volume fraction of hard carbide is 5-95%, with 5-20% in the top layer and 80-95% in the bottom layer; the volume fraction of hard carbide increases by 5-25% layer by layer from the top to the bottom layer. The cemented carbide in the diamond / hard alloy gradient transition layer is Co-WC, wherein the volume fraction of Co is 3% to 11%, and the Co content in the diamond / hard alloy gradient transition layer is equal to the Co content of the outermost layer of the gradient cemented carbide substrate. The number of layers in the diamond / hard alloy gradient transition layer is 4 to 15. In the diamond / hard alloy gradient transition layer, the thickness of each layer is 0.05 to 0.2 mm, and the total thickness is 0.2 to 3 mm.

4. A diamond / carbide composite tooth with a dual-gradient structure according to claim 1 or 2, characterized in that: In the gradient cemented carbide substrate, the volume fraction of WC is 65-97%, with 89-97% in the outermost layer and 65-81% in the innermost layer. The volume fraction of WC decreases by 1-10% from the outermost to the innermost layer. In the gradient cemented carbide substrate, the volume fraction of Co is 3-35%, with 3-11% in the outermost layer and 19-35% in the innermost layer. The volume fraction of Co increases by 1-10% from the outermost to the innermost layer. In the gradient cemented carbide substrate, a cemented carbide layer with a Co volume fraction of 11% is bonded to the bottom layer of the diamond / cemented carbide gradient transition layer. In the gradient cemented carbide substrate, the number of cemented carbide layers coaxially nested from the inside to the outside is 3 to 15. The thickness of each cemented carbide layer is 0.05 to 4 mm.

5. A diamond / carbide composite tooth with a dual-gradient structure according to claim 4, characterized in that: The thickness of the cemented carbide layer decreases sequentially from the inside to the outside; In the gradient cemented carbide substrate, the maximum outer diameter of the hemispherical segment is smaller than the outer diameter of the cylinder, and the upper end face of the cylinder extends radially outward beyond the bottom surface of the hemispherical segment to form a radial step, which matches the lower end of the spherical shell of the diamond / hard carbide gradient transition layer. The gradient hard alloy substrate consists of a central core, an intermediate nested layer, and an outer nested layer from the inside out. The central core is composed of a solid cylinder and a coaxially connected hemispherical core. The intermediate nested layer is composed of multiple layers of solid cylindrical tubes nested outwards and a spherical shell coaxially connected to the solid cylindrical tubes with the same thickness. The outer nested layer is composed of solid cylindrical tubes nested outwards. In the outer nested layer, the thickness of each solid cylindrical tube is 0.05 to 1 mm, and in the middle nested layer, the thickness of each solid cylindrical tube is ≥1 mm. In the outer nested layer, the volume fraction of Co is <11%, while in the middle nested layer, the volume fraction of Co is ≥11%. The curvature of the diamond / hard alloy gradient layer gradually decreases from the top to the bottom, and the curvature of each spherical shell of the gradient hard alloy substrate is the same.

6. A method for preparing a diamond / hard alloy composite tooth with a dual gradient structure as described in any one of claims 1-5, characterized in that: Based on the composition of the gradient cemented carbide substrate, WC powder, Co powder, and binder A are mixed to obtain n groups of gradient cemented carbide mixtures with different proportions. These n groups of gradient cemented carbide mixtures are then subjected to mixing, granulation, and wire drawing to obtain n groups of gradient cemented carbide wires. These n groups of gradient cemented carbide wires are then used in a layer-by-layer printing process to obtain a gradient cemented carbide green blank. Based on the composition of the diamond / cemented carbide gradient transition layer, polycrystalline diamond powder, WC-Co cemented carbide powder, and binder B are mixed to obtain m groups of diamond / cemented carbide gradient transition layer mixtures with different proportions. These m groups of diamond / cemented carbide gradient transition layer mixtures are then subjected to mixing, granulation, and wire drawing to obtain m groups of diamond / cemented carbide gradient transition layer wires. These m groups of diamond / cemented carbide gradient transition layer wires are then used in a layer-by-layer printing process to obtain a diamond / cemented carbide transition layer. Layered green blanks: Polycrystalline diamond and binder C are mixed to obtain a polycrystalline diamond layer mixture. The polycrystalline diamond layer mixture is then subjected to intensive mixing, granulation, and wire drawing to obtain polycrystalline diamond layer wires. The polycrystalline diamond layer wires are then printed to obtain polycrystalline diamond green blanks. Gradient cemented carbide green blanks are degreased to obtain degreased gradient cemented carbide blanks. The degreased gradient cemented carbide blanks are then sintered to obtain sintered gradient cemented carbide blanks. Diamond / cemented carbide transition layer green blanks and polycrystalline diamond green blanks are degreased to obtain degreased diamond / cemented carbide transition layer blanks and degreased polycrystalline diamond blanks, respectively. Then, according to the structure of diamond / cemented carbide composite teeth, the sintered gradient cemented carbide blanks, degreased diamond / cemented carbide transition layer blanks, and degreased polycrystalline diamond blanks are assembled in a bottom-to-top order and then synthesized under high temperature and high pressure to obtain diamond / cemented carbide composite teeth.

7. The method for preparing a diamond / carbide composite tooth with a dual gradient structure according to claim 6, characterized in that: The polydiamond powder has a particle size of 1–50 μm, the WC powder has a particle size of 5–200 μm, and the Co powder has a particle size of 1–100 μm. The adhesive A, by mass percentage, consists of the following components: 20-45% polyethylene, 20-35% paraffin wax, 8-12% microcrystalline wax, 8-12% polymethyl methacrylate, 12-15% ethylene-vinyl acetate copolymer, 2-3% epoxidized soybean oil, 1-3% stearic acid, and 1-2% butylated hydroxytoluene. In the n-group gradient cemented carbide mixture, the total mass ratio of WC powder and Co powder to the mass ratio of binder A is 1~6:1; When n groups of gradient cemented carbide mixtures are sequentially subjected to mixing, granulation, and wire drawing to obtain n groups of gradient cemented carbide wires, the mixing temperature is controlled at 160–200℃, the rotation speed at 30–60 r / min, and the time at 60–90 min; the granulation temperature is controlled at 160–200℃, the rotation speed at 30–60 r / min, and the wire drawing temperature is controlled at 180–220℃, and the wire drawing machine rotation speed at 40–50 rpm. The diameter of each of the n groups of gradient cemented carbide wires is 1.70–1.85 mm. When the n groups of gradient cemented carbide wires are printed to obtain gradient cemented carbide green blanks, the printing layer height is controlled to be 0.05-2 mm, the nozzle diameter is 0.2-0.4 mm, the nozzle temperature is 180-220℃, the printing speed is 50-150 mm / s, the printing temperature is 80-120℃, and the extrusion flow rate is 100-200%. The adhesive B, by weight percentage, consists of the following components: 25-35% polyethylene, 20-35% polymethyl methacrylate, 15-25% ethylene-vinyl acetate copolymer, 10-12% paraffin wax, 3-5% vinyl bis-stearamide, 2-3% stearic acid, and 1-2% dioctyl phthalate. In the m-group diamond / hard alloy gradient transition layer mixture, the total mass ratio of polycrystalline diamond powder and hard alloy powder to the mass ratio of binder B is 1~8:

1. When obtaining m-group diamond / hard alloy gradient transition layer wires by mixing, granulating, and drawing the mixtures, the mixing temperature is controlled at 160–200℃, the rotation speed at 30–60 r / min, and the time at 60–90 min; the granulation temperature is controlled at 160–200℃, the rotation speed at 30–60 r / min; the drawing temperature is controlled at 180–220℃, and the drawing machine rotation speed at 40–50 rpm. The diameter of the m-group diamond / hard alloy gradient transition layer wires is 1.70–1.85 mm. When preparing a diamond / hard alloy transition layer green body by printing m groups of diamond / hard alloy gradient transition layer wires, the printing layer height is controlled to be 0.05–2 mm, the nozzle diameter to be 0.2–0.4 mm, the nozzle temperature to be 180–220 °C, the printing speed to be 50–150 mm / s, the printing temperature to be 80–120 °C, and the extrusion flow rate to be 100–200%. The adhesive C, by mass percentage, comprises the following components: 15-25% polyethylene, 25-40% paraffin wax, 12-20% ethylene-vinyl acetate copolymer, 8-15% polyethylene glycol, 2-4% stearic acid, 3-8% microcrystalline wax, 2-5% epoxidized soybean oil, and 0.5-1.5% butylated hydroxytoluene. In the polycrystalline diamond layer mixture, the ratio of binder C to polycrystalline diamond powder is 1:1 to 10 by mass. When polycrystalline diamond layer mixtures are subjected to intensive mixing, granulation, and wire drawing to obtain polycrystalline diamond layer wires, the intensive mixing temperature is controlled at 160–200℃, the rotation speed at 30–60 r / min, and the time at 60–90 min; the granulation temperature is controlled at 160–200℃, the rotation speed at 30–60 r / min; the wire drawing temperature is controlled at 180–220℃, and the wire drawing machine rotation speed at 40–50 rpm; the diameter of the polycrystalline diamond layer wires is 1.70–1.85 mm. When the polycrystalline diamond layer filament is printed to obtain a polycrystalline diamond green blank, the printing layer height is controlled to be 0.05-2 mm, the nozzle diameter is 0.2-0.4 mm, the nozzle temperature is 180-220℃, the printing speed is 50-150 mm / s, the printing temperature is 80-120℃, and the extrusion flow rate is 100-200%.

8. The method for preparing a diamond / carbide composite tooth with a dual gradient structure according to claim 6, characterized in that: The degreasing process for gradient cemented carbide green blanks, diamond / cemented carbide transition layer green blanks, and polycrystalline diamond green blanks is as follows: first, heat from room temperature to 120–160°C at a heating rate of 4–10°C / min and hold for 60–120 min; then heat to 250–300°C at a heating rate of 3–8°C / min and hold for 90–120 min; then heat to 350–450°C at a heating rate of 2–6°C / min and hold for 60–90 min; finally, heat to 550–600°C at a heating rate of 1–3°C / min and hold for 90–120 min.

9. A method for preparing a diamond / hard alloy composite tooth with a dual gradient structure according to claim 6, characterized in that: The degreased graded cemented carbide blank is placed in a hot isostatic pressing furnace for sintering. The sintering process is as follows: first, the temperature is raised to 1300-1500℃ and sintered under vacuum for 60-90 minutes; then, argon gas is used as the pressure medium and hot isostatic pressing is performed at a pressing pressure of 6-8 MPa for 30-60 minutes.

10. The method for preparing a diamond / hard alloy composite tooth with a dual gradient structure according to claim 6, characterized in that: During the high-temperature and high-pressure synthesis, the pressure is controlled at 5–8 GPa, the temperature at 1400–1800 °C, and the time at 10–20 min.

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